diff --git a/.github/dependabot.yml b/.github/dependabot.yml
new file mode 100644
index 0000000..801aae8
--- /dev/null
+++ b/.github/dependabot.yml
@@ -0,0 +1,25 @@
+version: 2
+updates:
+  # Dart/Flutter dependencies (pubspec.yaml)
+  - package-ecosystem: "pub"
+    directory: "/"
+    schedule:
+      interval: "cron"
+      cronjob: "0 0 * * 2,5"
+      timezone: "Etc/UTC"
+    open-pull-requests-limit: 10
+    labels:
+      - "dependencies"
+      - "dart"
+
+  # GitHub Actions
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "cron"
+      cronjob: "0 0 * * 2,5"
+      timezone: "Etc/UTC"
+    open-pull-requests-limit: 5
+    labels:
+      - "dependencies"
+      - "github-actions"
diff --git a/.github/workflows/pr-unit-tests.yml b/.github/workflows/pr-unit-tests.yml
new file mode 100644
index 0000000..4e7fcef
--- /dev/null
+++ b/.github/workflows/pr-unit-tests.yml
@@ -0,0 +1,65 @@
+name: Run unit tests on Pull Request
+
+on:
+  pull_request:
+    branches:
+      - main
+    types: [opened, synchronize, reopened]
+
+permissions:
+  contents: read
+  checks: write
+  pull-requests: write
+
+concurrency:
+  group: "pr-unit-tests"
+  cancel-in-progress: false
+
+jobs:
+  unit-tests:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: .
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        continue-on-error: true
+        id: checkout_https
+
+      - name: Checkout repository via SSH (fallback)
+        if: steps.checkout_https.outcome == 'failure'
+        uses: actions/checkout@v4
+        with:
+          ssh-key: ${{ secrets.SSH_PRIVATE_KEY }}
+          ssh-strict: false
+
+      - name: Setup Flutter
+        uses: subosito/flutter-action@v2
+        with:
+          channel: stable
+          cache: true
+
+      - name: Install dependencies
+        run: flutter pub get
+
+      - name: Run build_runner (if needed)
+        run: flutter pub run build_runner build --delete-conflicting-outputs
+
+      - name: Run static analysis (for logs)
+        run: flutter analyze || true
+
+      - name: Setup reviewdog
+        uses: reviewdog/action-setup@v1
+        with:
+          reviewdog_version: latest
+
+      - name: Annotate analyzer results with reviewdog
+        env:
+          REVIEWDOG_GITHUB_API_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          # run analyzer and pipe into reviewdog so PRs get inline annotations
+          flutter analyze 2>&1 | reviewdog -efm="%f:%l:%c: %m" -name="flutter analyze" -reporter=github-pr-check -filter-mode=added -level=warning || true          
+
+      # - name: Run tests
+      #   run: flutter test
\ No newline at end of file
diff --git a/lib/data/repositories/document_repository.dart b/lib/data/repositories/document_repository.dart
index ae69d39..d60d7b9 100644
--- a/lib/data/repositories/document_repository.dart
+++ b/lib/data/repositories/document_repository.dart
@@ -8,12 +8,14 @@ import 'package:pdfrx/pdfrx.dart';
 
 import '../../domain/models/model.dart';
 
-class DocumentStateNotifier extends StateNotifier<Document> {
-  DocumentStateNotifier({ExportService? service})
-    : _service = service ?? ExportService(),
-      super(Document.initial());
+class DocumentStateNotifier extends Notifier<Document> {
+  late final ExportService _service;
 
-  final ExportService _service;
+  @override
+  Document build() {
+    _service = ExportService();
+    return Document.initial();
+  }
 
   @visibleForTesting
   void openSample() {
@@ -278,8 +280,8 @@ class DocumentStateNotifier extends StateNotifier<Document> {
 }
 
 final documentRepositoryProvider =
-    StateNotifierProvider<DocumentStateNotifier, Document>(
-      (ref) => DocumentStateNotifier(),
+    NotifierProvider<DocumentStateNotifier, Document>(
+      DocumentStateNotifier.new,
     );
 
 /// --- Isolate helpers of DocumentRepository ---
diff --git a/lib/data/repositories/preferences_repository.dart b/lib/data/repositories/preferences_repository.dart
index 2330d95..6cf4212 100644
--- a/lib/data/repositories/preferences_repository.dart
+++ b/lib/data/repositories/preferences_repository.dart
@@ -89,9 +89,39 @@ String _normalizeLanguageTag(String tag) {
   return tags.contains('en') ? 'en' : tags.first;
 }
 
-class PreferencesStateNotifier extends StateNotifier<PreferencesState> {
+class PreferencesStateNotifier extends Notifier<PreferencesState> {
   late final SharedPreferences _prefs;
   final Completer<void> _ready = Completer<void>();
+
+  @override
+  PreferencesState build() {
+    // Initialize with defaults
+    final defaultState = PreferencesState(
+      theme: 'system',
+      language: _normalizeLanguageTag(
+        WidgetsBinding.instance.platformDispatcher.locale.toLanguageTag(),
+      ),
+      exportDpi: 144.0,
+      theme_color: '#FF2196F3', // blue
+    );
+    // Start async initialization
+    _initAsync();
+    return defaultState;
+  }
+
+  void _initAsync() async {
+    _prefs = await SharedPreferences.getInstance();
+    await _load();
+    _ready.complete();
+  }
+
+  // For testing - can be called with mock SharedPreferences
+  void initWithPrefs(SharedPreferences prefs) {
+    _prefs = prefs;
+    _load();
+    _ready.complete();
+  }
+
   static Color? _tryParseColor(String? s) {
     if (s == null || s.isEmpty) return null;
     final v = s.trim();
@@ -162,22 +192,7 @@ class PreferencesStateNotifier extends StateNotifier<PreferencesState> {
     return '#$a$r$g$b';
   }
 
-  PreferencesStateNotifier([SharedPreferences? prefs])
-    : super(
-        PreferencesState(
-          theme: 'system',
-          language: _normalizeLanguageTag(
-            WidgetsBinding.instance.platformDispatcher.locale.toLanguageTag(),
-          ),
-          exportDpi: 144.0,
-          theme_color: '#FF2196F3', // blue
-        ),
-      ) {
-    _init(prefs);
-  }
-
-  Future<void> _init(SharedPreferences? injected) async {
-    _prefs = injected ?? await SharedPreferences.getInstance();
+  Future<void> _load() async {
     // Load persisted values (with sane defaults)
     final loaded = PreferencesState(
       theme: _prefs.getString(_kTheme) ?? 'system',
@@ -291,9 +306,8 @@ class PreferencesStateNotifier extends StateNotifier<PreferencesState> {
 }
 
 final preferencesRepositoryProvider =
-    StateNotifierProvider<PreferencesStateNotifier, PreferencesState>((ref) {
-      // Construct with lazy SharedPreferences initialization.
-      return PreferencesStateNotifier();
-    });
+    NotifierProvider<PreferencesStateNotifier, PreferencesState>(
+      PreferencesStateNotifier.new,
+    );
 
 // pageViewModeProvider removed; the app always runs in continuous mode.
diff --git a/lib/data/repositories/signature_asset_repository.dart b/lib/data/repositories/signature_asset_repository.dart
index d57037c..cf4bd39 100644
--- a/lib/data/repositories/signature_asset_repository.dart
+++ b/lib/data/repositories/signature_asset_repository.dart
@@ -3,8 +3,9 @@ import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:pdf_signature/domain/models/model.dart';
 
 ///
-class SignatureAssetRepository extends StateNotifier<List<SignatureAsset>> {
-  SignatureAssetRepository() : super(const []);
+class SignatureAssetRepository extends Notifier<List<SignatureAsset>> {
+  @override
+  List<SignatureAsset> build() => const [];
 
   /// Preferred API: add from an already decoded image to avoid re-decodes.
   void addImage(img.Image image, {String? name}) {
@@ -17,6 +18,6 @@ class SignatureAssetRepository extends StateNotifier<List<SignatureAsset>> {
 }
 
 final signatureAssetRepositoryProvider =
-    StateNotifierProvider<SignatureAssetRepository, List<SignatureAsset>>(
-      (ref) => SignatureAssetRepository(),
+    NotifierProvider<SignatureAssetRepository, List<SignatureAsset>>(
+      SignatureAssetRepository.new,
     );
diff --git a/lib/data/repositories/signature_card_repository.dart b/lib/data/repositories/signature_card_repository.dart
index 6820235..e31507b 100644
--- a/lib/data/repositories/signature_card_repository.dart
+++ b/lib/data/repositories/signature_card_repository.dart
@@ -54,8 +54,9 @@ class CachedSignatureCard {
       );
 }
 
-class SignatureCardStateNotifier extends StateNotifier<List<SignatureCard>> {
-  SignatureCardStateNotifier() : super(const []);
+class SignatureCardStateNotifier extends Notifier<List<SignatureCard>> {
+  @override
+  List<SignatureCard> build() => const [];
 
   // Internal storage with cache
   final List<CachedSignatureCard> _cards = <CachedSignatureCard>[];
@@ -207,6 +208,6 @@ class SignatureCardStateNotifier extends StateNotifier<List<SignatureCard>> {
 }
 
 final signatureCardRepositoryProvider =
-    StateNotifierProvider<SignatureCardStateNotifier, List<SignatureCard>>(
-      (ref) => SignatureCardStateNotifier(),
+    NotifierProvider<SignatureCardStateNotifier, List<SignatureCard>>(
+      SignatureCardStateNotifier.new,
     );
diff --git a/lib/routing/router.dart b/lib/routing/router.dart
index 8c489b6..cbf4528 100644
--- a/lib/routing/router.dart
+++ b/lib/routing/router.dart
@@ -26,15 +26,16 @@ final routerProvider = Provider<GoRouter>((ref) {
       GoRoute(
         path: '/',
         builder: (context, state) {
-          final sessionVm = ref.read(pdfSessionViewModelProvider(router));
+          final sessionVm = ref.read(pdfSessionViewModelProvider.notifier);
           return WelcomeScreen(
-            onPickPdf: () => sessionVm.pickAndOpenPdf(),
+            onPickPdf: () => sessionVm.pickAndOpenPdf(router),
             onOpenPdf:
                 ({String? path, Uint8List? bytes, String? fileName}) =>
                     sessionVm.openPdf(
                       path: path,
                       bytes: bytes ?? Uint8List(0),
                       fileName: fileName,
+                      router: router,
                     ),
           );
         },
@@ -42,12 +43,13 @@ final routerProvider = Provider<GoRouter>((ref) {
       GoRoute(
         path: '/pdf',
         builder: (context, state) {
-          final sessionVm = ref.read(pdfSessionViewModelProvider(router));
+          final sessionVm = ref.read(pdfSessionViewModelProvider.notifier);
+          final sessionState = ref.read(pdfSessionViewModelProvider);
           return PdfSignatureHomePage(
-            onPickPdf: () => sessionVm.pickAndOpenPdf(),
-            onClosePdf: () => sessionVm.closePdf(),
-            currentFile: sessionVm.currentFile,
-            currentFileName: sessionVm.displayFileName,
+            onPickPdf: () => sessionVm.pickAndOpenPdf(router),
+            onClosePdf: () => sessionVm.closePdf(router),
+            currentFile: sessionState.currentFile,
+            currentFileName: sessionState.displayFileName,
           );
         },
       ),
diff --git a/lib/ui/features/pdf/view_model/pdf_export_state.dart b/lib/ui/features/pdf/view_model/pdf_export_state.dart
new file mode 100644
index 0000000..09eaa94
--- /dev/null
+++ b/lib/ui/features/pdf/view_model/pdf_export_state.dart
@@ -0,0 +1,14 @@
+/// Immutable state for PdfExportViewModel
+class PdfExportState {
+  final bool exporting;
+
+  const PdfExportState({required this.exporting});
+
+  factory PdfExportState.initial() {
+    return const PdfExportState(exporting: false);
+  }
+
+  PdfExportState copyWith({bool? exporting}) {
+    return PdfExportState(exporting: exporting ?? this.exporting);
+  }
+}
diff --git a/lib/ui/features/pdf/view_model/pdf_export_view_model.dart b/lib/ui/features/pdf/view_model/pdf_export_view_model.dart
index dda891c..13e5f7e 100644
--- a/lib/ui/features/pdf/view_model/pdf_export_view_model.dart
+++ b/lib/ui/features/pdf/view_model/pdf_export_view_model.dart
@@ -5,39 +5,30 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:pdf_signature/data/repositories/document_repository.dart';
+import 'package:pdf_signature/ui/features/pdf/view_model/pdf_export_state.dart';
 
 /// ViewModel for export-related UI state and helpers.
-class PdfExportViewModel extends ChangeNotifier {
-  final Ref ref;
-  bool _exporting = false;
-
+class PdfExportViewModel extends Notifier<PdfExportState> {
   // Dependencies (injectable via constructor for tests)
   // Zero-arg picker retained for backward compatibility with tests.
-  final Future<String?> Function() _savePathPicker;
+  late final Future<String?> Function() _savePathPicker;
   // Preferred picker that accepts a suggested filename.
-  final Future<String?> Function(String suggestedName)
+  late final Future<String?> Function(String suggestedName)
   _savePathPickerWithSuggestedName;
 
-  PdfExportViewModel(
-    this.ref, {
-    Future<String?> Function()? savePathPicker,
-    Future<String?> Function(String suggestedName)?
-    savePathPickerWithSuggestedName,
-  }) : _savePathPicker = savePathPicker ?? _defaultSavePathPicker,
-       // Prefer provided suggested-name picker; otherwise, if only zero-arg
-       // picker is given (tests), wrap it; else use default that honors name.
-       _savePathPickerWithSuggestedName =
-           savePathPickerWithSuggestedName ??
-           (savePathPicker != null
-               ? ((_) => savePathPicker())
-               : _defaultSavePathPickerWithSuggestedName);
+  @override
+  PdfExportState build() {
+    // Initialize with default pickers
+    _savePathPicker = _defaultSavePathPicker;
+    _savePathPickerWithSuggestedName = _defaultSavePathPickerWithSuggestedName;
+    return PdfExportState.initial();
+  }
 
-  bool get exporting => _exporting;
+  bool get exporting => state.exporting;
 
   void setExporting(bool value) {
-    if (_exporting == value) return;
-    _exporting = value;
-    notifyListeners();
+    if (state.exporting == value) return;
+    state = state.copyWith(exporting: value);
   }
 
   /// Perform export via document repository. Returns true on success.
@@ -122,8 +113,7 @@ class PdfExportViewModel extends ChangeNotifier {
   }
 }
 
-final pdfExportViewModelProvider = ChangeNotifierProvider<PdfExportViewModel>((
-  ref,
-) {
-  return PdfExportViewModel(ref);
-});
+final pdfExportViewModelProvider =
+    NotifierProvider<PdfExportViewModel, PdfExportState>(
+      PdfExportViewModel.new,
+    );
diff --git a/lib/ui/features/pdf/view_model/pdf_session_state.dart b/lib/ui/features/pdf/view_model/pdf_session_state.dart
new file mode 100644
index 0000000..f5dd9d8
--- /dev/null
+++ b/lib/ui/features/pdf/view_model/pdf_session_state.dart
@@ -0,0 +1,23 @@
+import 'package:cross_file/cross_file.dart';
+
+/// Immutable state for PdfSessionViewModel
+class PdfSessionState {
+  final XFile currentFile;
+  final String displayFileName;
+
+  const PdfSessionState({
+    required this.currentFile,
+    required this.displayFileName,
+  });
+
+  factory PdfSessionState.initial() {
+    return PdfSessionState(currentFile: XFile(''), displayFileName: '');
+  }
+
+  PdfSessionState copyWith({XFile? currentFile, String? displayFileName}) {
+    return PdfSessionState(
+      currentFile: currentFile ?? this.currentFile,
+      displayFileName: displayFileName ?? this.displayFileName,
+    );
+  }
+}
diff --git a/lib/ui/features/pdf/view_model/pdf_view_model.dart b/lib/ui/features/pdf/view_model/pdf_view_model.dart
index c0c58fc..f993204 100644
--- a/lib/ui/features/pdf/view_model/pdf_view_model.dart
+++ b/lib/ui/features/pdf/view_model/pdf_view_model.dart
@@ -7,103 +7,70 @@ import 'package:pdf_signature/data/repositories/document_repository.dart';
 import 'package:pdf_signature/data/repositories/signature_card_repository.dart';
 import 'package:pdf_signature/domain/models/model.dart';
 import 'package:pdf_signature/ui/features/pdf/view_model/document_version.dart';
+import 'package:pdf_signature/ui/features/pdf/view_model/pdf_view_state.dart';
+import 'package:pdf_signature/ui/features/pdf/view_model/pdf_session_state.dart';
 import 'package:pdfrx/pdfrx.dart';
 import 'package:file_picker/file_picker.dart' as fp;
 import 'package:go_router/go_router.dart';
 import 'package:path_provider/path_provider.dart';
 import 'package:flutter/foundation.dart';
 
-class PdfViewModel extends ChangeNotifier {
-  final Ref ref;
-  PdfViewerController _controller = PdfViewerController();
-  PdfViewerController get controller => _controller;
-  int _currentPage = 1;
-  late final bool _useMockViewer;
-  bool _isDisposed = false;
-
-  // Active rect for signature placement overlay
-  Rect? _activeRect;
-  Rect? get activeRect => _activeRect;
-  set activeRect(Rect? value) {
-    _activeRect = value;
-    if (!_isDisposed) {
-      notifyListeners();
-    }
+class PdfViewModel extends Notifier<PdfViewState> {
+  @override
+  PdfViewState build() {
+    return PdfViewState.initial();
   }
 
-  // Locked placements: Set of (page, index) tuples
-  final Set<String> _lockedPlacements = {};
-  Set<String> get lockedPlacements => Set.unmodifiable(_lockedPlacements);
+  PdfViewerController get controller => state.controller;
+  int get currentPage => state.currentPage;
+  bool get useMockViewer => state.useMockViewer;
+  Rect? get activeRect => state.activeRect;
+  Set<String> get lockedPlacements => state.lockedPlacements;
 
-  // Document version tracking for UI consistency
-  DocumentVersion _documentVersion = DocumentVersion.initial();
+  set activeRect(Rect? value) {
+    state = state.copyWith(activeRect: value, clearActiveRect: value == null);
+  }
+
+  set currentPage(int value) {
+    final doc = ref.read(documentRepositoryProvider);
+    final clamped = value.clamp(1, doc.pageCount);
+    debugPrint('PdfViewModel.currentPage set to $clamped');
+    state = state.copyWith(currentPage: clamped);
+  }
 
   // Get current document source name for PdfDocumentRefData
   String get documentSourceName {
     // Ensure document version is up to date, but only update if really needed
     _updateDocumentVersionIfNeeded();
-    return _documentVersion.sourceName;
+    return state.documentVersion.sourceName;
   }
 
   void _updateDocumentVersionIfNeeded() {
     final document = ref.read(documentRepositoryProvider);
-    if (!identical(_documentVersion.lastBytes, document.pickedPdfBytes)) {
-      _documentVersion = DocumentVersion(
-        version: _documentVersion.version + 1,
-        lastBytes: document.pickedPdfBytes,
+    if (!identical(state.documentVersion.lastBytes, document.pickedPdfBytes)) {
+      state = state.copyWith(
+        documentVersion: DocumentVersion(
+          version: state.documentVersion.version + 1,
+          lastBytes: document.pickedPdfBytes,
+        ),
       );
     }
   }
 
-  // const bool.fromEnvironment('FLUTTER_TEST', defaultValue: false);
-  PdfViewModel(this.ref, {bool? useMockViewer})
-    : _useMockViewer =
-          useMockViewer ??
-          const bool.fromEnvironment('FLUTTER_TEST', defaultValue: false);
-
-  bool get useMockViewer => _useMockViewer;
-
-  int get currentPage => _currentPage;
-
-  set currentPage(int value) {
-    _currentPage = value.clamp(1, document.pageCount);
-    // ignore: avoid_print
-    debugPrint('PdfViewModel.currentPage set to $_currentPage');
-    if (!_isDisposed) {
-      notifyListeners();
-    }
-  }
-
   // Do not watch the document repository here; watching would cause this
-  // ChangeNotifier to be disposed/recreated on every document change, which
+  // notifier to be disposed/recreated on every document change, which
   // resets transient UI state like locked placements. Read instead.
   Document get document => ref.read(documentRepositoryProvider);
 
   void jumpToPage(int page) {
-    // ignore: avoid_print
-    debugPrint('PdfViewModel.jumpToPage ' + page.toString());
+    debugPrint('PdfViewModel.jumpToPage $page');
     currentPage = page;
   }
 
-  // Make this view model "int-like" for tests that compare it directly to an
-  // integer or use it as a Map key for page lookups.
-  @override
-  bool operator ==(Object other) {
-    if (identical(this, other)) return true;
-    if (other is int) {
-      return other == currentPage;
-    }
-    return false;
-  }
-
-  @override
-  int get hashCode => currentPage.hashCode;
-
   // Allow repositories to request a UI refresh without mutating provider state
   void notifyPlacementsChanged() {
-    if (!_isDisposed) {
-      notifyListeners();
-    }
+    // Force a rebuild by updating state
+    state = state.copyWith();
   }
 
   // Document repository methods
@@ -146,10 +113,9 @@ class PdfViewModel extends ChangeNotifier {
         .read(documentRepositoryProvider.notifier)
         .removePlacement(page: page, index: index);
     // Also remove from locked placements if it was locked
-    _lockedPlacements.remove(_placementKey(page, index));
-    if (!_isDisposed) {
-      notifyListeners();
-    }
+    final newLocked = Set<String>.from(state.lockedPlacements)
+      ..remove(_placementKey(page, index));
+    state = state.copyWith(lockedPlacements: newLocked);
   }
 
   void updatePlacementRect({
@@ -177,23 +143,21 @@ class PdfViewModel extends ChangeNotifier {
 
   // Check if a placement is locked
   bool isPlacementLocked({required int page, required int index}) {
-    return _lockedPlacements.contains(_placementKey(page, index));
+    return state.lockedPlacements.contains(_placementKey(page, index));
   }
 
   // Lock a placement
   void lockPlacement({required int page, required int index}) {
-    _lockedPlacements.add(_placementKey(page, index));
-    if (!_isDisposed) {
-      notifyListeners();
-    }
+    final newLocked = Set<String>.from(state.lockedPlacements)
+      ..add(_placementKey(page, index));
+    state = state.copyWith(lockedPlacements: newLocked);
   }
 
   // Unlock a placement
   void unlockPlacement({required int page, required int index}) {
-    _lockedPlacements.remove(_placementKey(page, index));
-    if (!_isDisposed) {
-      notifyListeners();
-    }
+    final newLocked = Set<String>.from(state.lockedPlacements)
+      ..remove(_placementKey(page, index));
+    state = state.copyWith(lockedPlacements: newLocked);
   }
 
   // Toggle lock state of a placement
@@ -250,37 +214,24 @@ class PdfViewModel extends ChangeNotifier {
   void clearAllSignatureCards() {
     ref.read(signatureCardRepositoryProvider.notifier).clearAll();
   }
-
-  @override
-  void dispose() {
-    _isDisposed = true;
-    super.dispose();
-  }
 }
 
-final pdfViewModelProvider = ChangeNotifierProvider<PdfViewModel>((ref) {
-  return PdfViewModel(ref);
-});
+final pdfViewModelProvider = NotifierProvider<PdfViewModel, PdfViewState>(
+  PdfViewModel.new,
+);
 
 /// ViewModel managing PDF session lifecycle (file picking/open/close) and
 /// navigation. Replaces the previous PdfManager helper.
-class PdfSessionViewModel extends ChangeNotifier {
-  final Ref ref;
-  final GoRouter router;
-  XFile _currentFile = XFile('');
-  // Keep a human display name in addition to XFile, because on Linux via
-  // xdg-desktop-portal the path can look like /run/user/.../doc/<UUID>, and
-  // XFile.name derives from that basename, yielding a random UUID instead of
-  // the actual filename the user selected. We preserve the picker/drop name
-  // here to offer a sensible default like "signed_<original>.pdf".
-  String _displayFileName = '';
+class PdfSessionViewModel extends Notifier<PdfSessionState> {
+  @override
+  PdfSessionState build() {
+    return PdfSessionState.initial();
+  }
 
-  PdfSessionViewModel({required this.ref, required this.router});
+  XFile get currentFile => state.currentFile;
+  String get displayFileName => state.displayFileName;
 
-  XFile get currentFile => _currentFile;
-  String get displayFileName => _displayFileName;
-
-  Future<void> pickAndOpenPdf() async {
+  Future<void> pickAndOpenPdf(GoRouter router) async {
     final result = await fp.FilePicker.platform.pickFiles(
       type: fp.FileType.custom,
       allowedExtensions: const ['pdf'],
@@ -304,7 +255,12 @@ class PdfSessionViewModel extends ChangeNotifier {
       }
     }
     if (effectiveBytes != null) {
-      await openPdf(path: path, bytes: effectiveBytes, fileName: name);
+      await openPdf(
+        path: path,
+        bytes: effectiveBytes,
+        fileName: name,
+        router: router,
+      );
     } else {
       debugPrint(
         '[PdfSessionViewModel] No PDF data available to open (path=$path, name=$name)',
@@ -316,6 +272,7 @@ class PdfSessionViewModel extends ChangeNotifier {
     String? path,
     required Uint8List bytes,
     String? fileName,
+    required GoRouter router,
   }) async {
     int pageCount = 1; // default
     try {
@@ -355,36 +312,44 @@ class PdfSessionViewModel extends ChangeNotifier {
       );
       debugPrint(st.toString());
     }
+    XFile newFile;
     if (path != null && path.isNotEmpty) {
-      _currentFile = XFile(path);
+      newFile = XFile(path);
     } else if ((fileName != null && fileName.isNotEmpty)) {
       // Keep in-memory XFile so .name is available for suggestion
       try {
-        _currentFile = XFile.fromData(
+        newFile = XFile.fromData(
           bytes,
           name: fileName,
           mimeType: 'application/pdf',
         );
       } catch (e, st) {
-        _currentFile = XFile(fileName);
+        newFile = XFile(fileName);
         debugPrint(
           '[PdfSessionViewModel] Failed to create XFile.fromData name=$fileName error=$e',
         );
         debugPrint(st.toString());
       }
     } else {
-      _currentFile = XFile('');
+      newFile = XFile('');
     }
 
     // Update display name: prefer explicit fileName (from picker/drop),
     // fall back to basename of path, otherwise empty.
+    String newDisplayFileName;
     if (fileName != null && fileName.isNotEmpty) {
-      _displayFileName = fileName;
+      newDisplayFileName = fileName;
     } else if (path != null && path.isNotEmpty) {
-      _displayFileName = path.split('/').last.split('\\').last;
+      newDisplayFileName = path.split('/').last.split('\\').last;
     } else {
-      _displayFileName = '';
+      newDisplayFileName = '';
     }
+
+    state = state.copyWith(
+      currentFile: newFile,
+      displayFileName: newDisplayFileName,
+    );
+
     // If fast path failed to set repository (e.g., exception earlier), fallback to async derive.
     if (ref.read(documentRepositoryProvider).pickedPdfBytes != bytes) {
       debugPrint(
@@ -397,21 +362,18 @@ class PdfSessionViewModel extends ChangeNotifier {
     // relies on this behavior. Placements are reset by openPicked() above.
     debugPrint('[PdfSessionViewModel] Navigating to /pdf');
     router.go('/pdf');
-    debugPrint('[PdfSessionViewModel] Notifying listeners after open');
-    notifyListeners();
+    debugPrint('[PdfSessionViewModel] State updated after open');
   }
 
-  void closePdf() {
+  void closePdf(GoRouter router) {
     ref.read(documentRepositoryProvider.notifier).close();
     ref.read(signatureCardRepositoryProvider.notifier).clearAll();
-    _currentFile = XFile('');
-    _displayFileName = '';
+    state = state.copyWith(currentFile: XFile(''), displayFileName: '');
     router.go('/');
-    notifyListeners();
   }
 }
 
 final pdfSessionViewModelProvider =
-    ChangeNotifierProvider.family<PdfSessionViewModel, GoRouter>((ref, router) {
-      return PdfSessionViewModel(ref: ref, router: router);
-    });
+    NotifierProvider<PdfSessionViewModel, PdfSessionState>(
+      PdfSessionViewModel.new,
+    );
diff --git a/lib/ui/features/pdf/view_model/pdf_view_state.dart b/lib/ui/features/pdf/view_model/pdf_view_state.dart
new file mode 100644
index 0000000..a7abe1c
--- /dev/null
+++ b/lib/ui/features/pdf/view_model/pdf_view_state.dart
@@ -0,0 +1,54 @@
+import 'package:flutter/material.dart';
+import 'package:pdf_signature/ui/features/pdf/view_model/document_version.dart';
+import 'package:pdfrx/pdfrx.dart';
+
+/// Immutable state for PdfViewModel
+class PdfViewState {
+  final PdfViewerController controller;
+  final int currentPage;
+  final bool useMockViewer;
+  final Rect? activeRect;
+  final Set<String> lockedPlacements;
+  final DocumentVersion documentVersion;
+
+  const PdfViewState({
+    required this.controller,
+    required this.currentPage,
+    required this.useMockViewer,
+    this.activeRect,
+    required this.lockedPlacements,
+    required this.documentVersion,
+  });
+
+  factory PdfViewState.initial({bool? useMockViewer}) {
+    return PdfViewState(
+      controller: PdfViewerController(),
+      currentPage: 1,
+      useMockViewer:
+          useMockViewer ??
+          const bool.fromEnvironment('FLUTTER_TEST', defaultValue: false),
+      activeRect: null,
+      lockedPlacements: const {},
+      documentVersion: DocumentVersion.initial(),
+    );
+  }
+
+  PdfViewState copyWith({
+    PdfViewerController? controller,
+    int? currentPage,
+    bool? useMockViewer,
+    Rect? activeRect,
+    bool clearActiveRect = false,
+    Set<String>? lockedPlacements,
+    DocumentVersion? documentVersion,
+  }) {
+    return PdfViewState(
+      controller: controller ?? this.controller,
+      currentPage: currentPage ?? this.currentPage,
+      useMockViewer: useMockViewer ?? this.useMockViewer,
+      activeRect: clearActiveRect ? null : (activeRect ?? this.activeRect),
+      lockedPlacements: lockedPlacements ?? this.lockedPlacements,
+      documentVersion: documentVersion ?? this.documentVersion,
+    );
+  }
+}
diff --git a/lib/ui/features/pdf/widgets/pdf_page_area.dart b/lib/ui/features/pdf/widgets/pdf_page_area.dart
index 1579dcf..626f6b2 100644
--- a/lib/ui/features/pdf/widgets/pdf_page_area.dart
+++ b/lib/ui/features/pdf/widgets/pdf_page_area.dart
@@ -112,11 +112,12 @@ class _PdfPageAreaState extends ConsumerState<PdfPageArea> {
 
   @override
   Widget build(BuildContext context) {
-    final pdfViewModel = ref.watch(pdfViewModelProvider);
+    final pdfViewState = ref.watch(pdfViewModelProvider);
+    final pdfViewModel = ref.read(pdfViewModelProvider.notifier);
     final pdf = pdfViewModel.document;
     const pageViewMode = 'continuous';
-    // React to PdfViewModel currentPage changes. With ChangeNotifierProvider,
-    // prev/next are the same instance, so compare to a local cache.
+    // React to PdfViewModel currentPage changes. With NotifierProvider,
+    // prev/next are now different state objects, so we can compare them directly.
     ref.listen(pdfViewModelProvider, (prev, next) {
       // Only perform manual scrolling in mock viewer mode. In real viewer mode,
       // PdfViewerController + onPageChanged keep things in sync, and attempting
diff --git a/lib/ui/features/pdf/widgets/pdf_page_overlays.dart b/lib/ui/features/pdf/widgets/pdf_page_overlays.dart
index c41bbf1..cbb53e3 100644
--- a/lib/ui/features/pdf/widgets/pdf_page_overlays.dart
+++ b/lib/ui/features/pdf/widgets/pdf_page_overlays.dart
@@ -36,12 +36,12 @@ class PdfPageOverlays extends ConsumerWidget {
     if (!overlaysEnabled) {
       return const SizedBox.shrink();
     }
-    final pdfViewModel = ref.watch(pdfViewModelProvider);
+    final pdfViewState = ref.watch(pdfViewModelProvider);
     // Subscribe to document changes to rebuild overlays
     final pdf = ref.watch(documentRepositoryProvider);
     final placed =
         pdf.placementsByPage[pageNumber] ?? const <SignaturePlacement>[];
-    final activeRect = pdfViewModel.activeRect;
+    final activeRect = pdfViewState.activeRect;
     final widgets = <Widget>[];
 
     // Base DragTarget filling the whole page to accept drops from signature cards.
@@ -116,10 +116,10 @@ class PdfPageOverlays extends ConsumerWidget {
 
     // TODO:Add active overlay if present and not using mock (mock has its own)
 
-    final useMock = pdfViewModel.useMockViewer;
+    final useMock = pdfViewState.useMockViewer;
     if (!useMock &&
         activeRect != null &&
-        pageNumber == pdfViewModel.currentPage) {
+        pageNumber == pdfViewState.currentPage) {
       widgets.add(
         LayoutBuilder(
           builder: (context, constraints) {
diff --git a/lib/ui/features/pdf/widgets/pdf_screen.dart b/lib/ui/features/pdf/widgets/pdf_screen.dart
index 2baa017..5b2e55d 100644
--- a/lib/ui/features/pdf/widgets/pdf_screen.dart
+++ b/lib/ui/features/pdf/widgets/pdf_screen.dart
@@ -195,7 +195,7 @@ class _PdfSignatureHomePageState extends ConsumerState<PdfSignatureHomePage> {
 
         if (!kIsWeb) {
           final path = await ref
-              .read(pdfExportViewModelProvider)
+              .read(pdfExportViewModelProvider.notifier)
               .pickSavePathWithSuggestedName(suggested);
           if (path == null || path.trim().isEmpty) return;
           final fullPath = _ensurePdfExtension(path.trim());
@@ -203,7 +203,7 @@ class _PdfSignatureHomePageState extends ConsumerState<PdfSignatureHomePage> {
           // ignore: avoid_print
           debugPrint('_saveSignedPdf: picked save path ' + fullPath);
           ok = await ref
-              .read(pdfExportViewModelProvider)
+              .read(pdfExportViewModelProvider.notifier)
               .exportToPath(
                 outputPath: fullPath,
                 uiPageSize: _pageSize,
@@ -329,7 +329,8 @@ class _PdfSignatureHomePageState extends ConsumerState<PdfSignatureHomePage> {
               }(),
               child: Consumer(
                 builder: (context, ref, child) {
-                  final pdfViewModel = ref.watch(pdfViewModelProvider);
+                  final pdfViewState = ref.watch(pdfViewModelProvider);
+                  final pdfViewModel = ref.read(pdfViewModelProvider.notifier);
                   final pdf = pdfViewModel.document;
 
                   final documentRef =
diff --git a/lib/ui/features/pdf/widgets/pdf_toolbar.dart b/lib/ui/features/pdf/widgets/pdf_toolbar.dart
index 362d4d5..0975a4b 100644
--- a/lib/ui/features/pdf/widgets/pdf_toolbar.dart
+++ b/lib/ui/features/pdf/widgets/pdf_toolbar.dart
@@ -59,11 +59,11 @@ class _PdfToolbarState extends ConsumerState<PdfToolbar> {
 
   @override
   Widget build(BuildContext context) {
-    final pdfViewModel = ref.watch(pdfViewModelProvider);
+    final pdfViewState = ref.watch(pdfViewModelProvider);
     final pdf = ref.watch(
       documentRepositoryProvider,
     ); // Watch document directly for updates
-    final currentPage = pdfViewModel.currentPage;
+    final currentPage = pdfViewState.currentPage;
     final l = AppLocalizations.of(context);
     final pageInfo = l.pageInfo(currentPage, pdf.pageCount);
 
diff --git a/lib/ui/features/pdf/widgets/pdf_viewer_widget.dart b/lib/ui/features/pdf/widgets/pdf_viewer_widget.dart
index dadf2d6..9298181 100644
--- a/lib/ui/features/pdf/widgets/pdf_viewer_widget.dart
+++ b/lib/ui/features/pdf/widgets/pdf_viewer_widget.dart
@@ -51,7 +51,7 @@ class _PdfViewerWidgetState extends ConsumerState<PdfViewerWidget> {
     final bytes = doc.pickedPdfBytes!;
     if (!identical(bytes, _lastBytes)) {
       _lastBytes = bytes;
-      final viewModel = ref.read(pdfViewModelProvider);
+      final viewModel = ref.read(pdfViewModelProvider.notifier);
       debugPrint(
         '[PdfViewerWidget] New PDF bytes detected -> ${viewModel.documentSourceName}',
       );
@@ -84,9 +84,9 @@ class _PdfViewerWidgetState extends ConsumerState<PdfViewerWidget> {
 
   @override
   Widget build(BuildContext context) {
-    final pdfViewModel = ref.watch(pdfViewModelProvider);
+    final pdfViewState = ref.watch(pdfViewModelProvider);
     final document = ref.watch(documentRepositoryProvider);
-    final useMock = pdfViewModel.useMockViewer;
+    final useMock = pdfViewState.useMockViewer;
     _updateDocRef(document);
 
     if (useMock) {
@@ -113,7 +113,7 @@ class _PdfViewerWidgetState extends ConsumerState<PdfViewerWidget> {
           }
           return Center(child: Text(text));
         }
-        final pdfViewModel = ref.read(pdfViewModelProvider);
+        final pdfViewModel = ref.read(pdfViewModelProvider.notifier);
         final viewerKey =
             widget.innerViewerKey ??
             Key('pdf_viewer_${pdfViewModel.documentSourceName}');
diff --git a/lib/ui/features/pdf/widgets/signature_overlay.dart b/lib/ui/features/pdf/widgets/signature_overlay.dart
index 905812e..2ad7f31 100644
--- a/lib/ui/features/pdf/widgets/signature_overlay.dart
+++ b/lib/ui/features/pdf/widgets/signature_overlay.dart
@@ -42,9 +42,10 @@ class SignatureOverlay extends ConsumerWidget {
 
         Future<void> _showContextMenu(Offset position) async {
           final pdfViewModel = ref.read(pdfViewModelProvider.notifier);
-          final isLocked = ref
-              .watch(pdfViewModelProvider)
-              .isPlacementLocked(page: pageNumber, index: placedIndex);
+          final isLocked = pdfViewModel.isPlacementLocked(
+            page: pageNumber,
+            index: placedIndex,
+          );
           final selected = await showMenu<String>(
             context: context,
             position: RelativeRect.fromLTRB(
@@ -92,7 +93,7 @@ class SignatureOverlay extends ConsumerWidget {
               allowContentFlipping: false,
               onChanged:
                   ref
-                          .watch(pdfViewModelProvider)
+                          .read(pdfViewModelProvider.notifier)
                           .isPlacementLocked(
                             page: pageNumber,
                             index: placedIndex,
@@ -118,7 +119,7 @@ class SignatureOverlay extends ConsumerWidget {
               // Keep default handles; you can customize later if needed
               contentBuilder: (context, boxRect, flip) {
                 final isLocked = ref
-                    .watch(pdfViewModelProvider)
+                    .read(pdfViewModelProvider.notifier)
                     .isPlacementLocked(page: pageNumber, index: placedIndex);
                 return DecoratedBox(
                   decoration: BoxDecoration(
diff --git a/lib/ui/features/signature/view_model/dragging_signature_view_model.dart b/lib/ui/features/signature/view_model/dragging_signature_view_model.dart
index dd13ebe..498470c 100644
--- a/lib/ui/features/signature/view_model/dragging_signature_view_model.dart
+++ b/lib/ui/features/signature/view_model/dragging_signature_view_model.dart
@@ -1,6 +1,14 @@
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 
 /// Global flag indicating whether a signature card is currently being dragged.
-final isDraggingSignatureViewModelProvider = StateProvider<bool>(
-  (ref) => false,
-);
+class IsDraggingSignatureNotifier extends Notifier<bool> {
+  @override
+  bool build() => false;
+
+  void setDragging(bool value) => state = value;
+}
+
+final isDraggingSignatureViewModelProvider =
+    NotifierProvider<IsDraggingSignatureNotifier, bool>(
+      IsDraggingSignatureNotifier.new,
+    );
diff --git a/lib/ui/features/signature/widgets/signature_card_view.dart b/lib/ui/features/signature/widgets/signature_card_view.dart
index ffd9c63..19c752d 100644
--- a/lib/ui/features/signature/widgets/signature_card_view.dart
+++ b/lib/ui/features/signature/widgets/signature_card_view.dart
@@ -158,10 +158,14 @@ class _SignatureCardViewState extends ConsumerState<SignatureCardView> {
         ),
       ),
       onDragStarted: () {
-        ref.read(isDraggingSignatureViewModelProvider.notifier).state = true;
+        ref
+            .read(isDraggingSignatureViewModelProvider.notifier)
+            .setDragging(true);
       },
       onDragEnd: (_) {
-        ref.read(isDraggingSignatureViewModelProvider.notifier).state = false;
+        ref
+            .read(isDraggingSignatureViewModelProvider.notifier)
+            .setDragging(false);
       },
       feedback: Opacity(
         opacity: 0.9,
diff --git a/lib/ui/features/welcome/view_model/welcome_view_model.dart b/lib/ui/features/welcome/view_model/welcome_view_model.dart
index 8a17753..e170807 100644
--- a/lib/ui/features/welcome/view_model/welcome_view_model.dart
+++ b/lib/ui/features/welcome/view_model/welcome_view_model.dart
@@ -20,8 +20,8 @@ class WelcomeViewModel {
     }
 
     // Use PdfSessionViewModel to open and navigate.
-    final session = ref.read(pdfSessionViewModelProvider(router));
-    await session.openPdf(path: path, bytes: bytes);
+    final session = ref.read(pdfSessionViewModelProvider.notifier);
+    await session.openPdf(path: path, bytes: bytes, router: router);
   }
 }
 
diff --git a/lib/ui/features/welcome/widgets/welcome_screen.dart b/lib/ui/features/welcome/widgets/welcome_screen.dart
index 6aab832..681ef13 100644
--- a/lib/ui/features/welcome/widgets/welcome_screen.dart
+++ b/lib/ui/features/welcome/widgets/welcome_screen.dart
@@ -25,9 +25,6 @@ class _DropReadableFromDesktop implements DropReadable {
   Future<Uint8List> readAsBytes() => inner.readAsBytes();
 }
 
-// Allow injecting Riverpod's read function from either WidgetRef or ProviderContainer
-typedef Reader = T Function<T>(ProviderListenable<T> provider);
-
 // Select first .pdf file (case-insensitive) or fall back to first entry.
 Future<void> handleDroppedFiles(
   Future<void> Function({String? path, Uint8List? bytes, String? fileName})
diff --git a/pubspec.yaml b/pubspec.yaml
index 3805788..d949a58 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -2,7 +2,7 @@ name: pdf_signature
 description: "A new Flutter project."
 # The following line prevents the package from being accidentally published to
 # pub.dev using `flutter pub publish`. This is preferred for private packages.
-publish_to: 'none' # Remove this line if you wish to publish to pub.dev
+publish_to: "none" # Remove this line if you wish to publish to pub.dev
 
 # The following defines the version and build number for your application.
 # A version number is three numbers separated by dots, like 1.2.43
@@ -42,28 +42,28 @@ dependencies:
   # The following adds the Cupertino Icons font to your application.
   # Use with the CupertinoIcons class for iOS style icons.
   cupertino_icons: ^1.0.8
-  flutter_riverpod: ^2.6.1
+  flutter_riverpod: ^3.0.3
   shared_preferences: ^2.5.3
   flutter_dotenv: ^6.0.0
   path_provider: ^2.1.5
-  pdfrx: ^2.1.9
+  pdfrx: ^2.2.16
   pdf: ^3.10.8
   # printing: ^5.14.2 # extension of pdf pkg
   hand_signature: ^3.1.0+2
   image: ^4.2.0
   result_dart: ^2.1.1
-  go_router: ^16.2.0
+  go_router: ^17.0.0
   flutter_localizations:
     sdk: flutter
   intl: any
   flutter_localized_locales: ^2.0.5
-  desktop_drop: ^0.6.1
+  desktop_drop: ^0.7.0
   multi_split_view: ^3.6.1
   freezed_annotation: ^3.1.0
   json_annotation: ^4.9.0
   share_plus: ^12.0.0
   logging: ^1.3.0
-  riverpod_annotation: ^2.6.1
+  riverpod_annotation: ^3.0.3
   colorfilter_generator: ^0.0.8
   flutter_box_transform: ^0.4.7
   file_picker: ^10.3.3
@@ -78,12 +78,12 @@ dev_dependencies:
   integration_test:
     sdk: flutter
   build_runner: ^2.4.12
-  build: ^3.0.2
-  bdd_widget_test: ^2.0.1
+  build: ^4.0.3
+  bdd_widget_test: ^2.1.3
   mocktail: ^1.0.4
   freezed: ^3.0.0
-  custom_lint: ^0.7.6
-  riverpod_lint: ^2.6.5
+  # custom_lint: ^0.7.6
+  # riverpod_lint: ^2.6.5
   go_router_builder: ^4.0.1
 
   # The "flutter_lints" package below contains a set of recommended lints to
@@ -141,7 +141,6 @@ flutter:
   # For details regarding fonts from package dependencies,
   # see https://flutter.dev/to/font-from-package
 
-
 flutter_launcher_icons:
   image_path: "assets/icon/pdf_signature-icon.png"
   android: true