Add support for existing reference objects

@@ -3,6 +3,7 @@
 ## 3.10.8
 
 - Add Flutter's Logical Pixel constant
+- Add support for existing reference objects
 
 ## 3.10.7
 

@@ -104,8 +104,10 @@ class PdfChoiceField extends PdfAnnotWidget {
 }
 
 class PdfAnnot extends PdfObject<PdfDict> {
-  PdfAnnot(this.pdfPage, this.annot)
+  PdfAnnot(this.pdfPage, this.annot, {int? objser, int objgen = 0})
       : super(pdfPage.pdfDocument,
+            objser: objser,
+            objgen: objgen,
             params: PdfDict.values({
               '/Type': const PdfName('/Annot'),
             })) {

@@ -142,7 +142,10 @@ class PdfCatalog extends PdfObject<PdfDict> {
           (acroForm['/SigFlags'] as PdfNum? ?? const PdfNum(0));
       final fields = (acroForm['/Fields'] ??= PdfArray()) as PdfArray;
       for (final w in widgets) {
-        fields.add(w.ref());
+        final ref = w.ref();
+        if (!fields.values.contains(ref)) {
+          fields.add(ref);
+        }
       }
     }
   }

@@ -19,6 +19,7 @@ import 'dart:math';
 import 'package:vector_math/vector_math_64.dart';
 
 import '../../pdf.dart';
+import '../pdf/format/indirect.dart';
 import 'geometry.dart';
 import 'shape.dart';
 import 'text_style.dart';
@@ -32,6 +33,7 @@ class Anchor extends SingleChildWidget {
     this.description,
     this.zoom,
     this.setX = false,
+    this.replaces,
   }) : super(child: child);
 
   final String name;
@@ -42,6 +44,8 @@ class Anchor extends SingleChildWidget {
 
   final bool setX;
 
+  final PdfIndirect? replaces;
+
   @override
   void paint(Context context) {
     super.paint(context);
@@ -60,7 +64,12 @@ class Anchor extends SingleChildWidget {
     if (description != null) {
       final rb = mat.transform3(Vector3(box!.right, box!.top, 0));
       final iBox = PdfRect.fromLTRB(lt.x, lt.y, rb.x, rb.y);
-      PdfAnnot(context.page, PdfAnnotText(rect: iBox, content: description!));
+      PdfAnnot(
+        context.page,
+        PdfAnnotText(rect: iBox, content: description!),
+        objser: replaces?.ser,
+        objgen: replaces?.gen ?? 0,
+      );
     }
   }
 }
@@ -70,10 +79,12 @@ abstract class AnnotationBuilder {
 }
 
 class AnnotationLink extends AnnotationBuilder {
-  AnnotationLink(this.destination);
+  AnnotationLink(this.destination, {this.replaces});
 
   final String destination;
 
+  final PdfIndirect? replaces;
+
   @override
   PdfAnnot build(Context context, PdfRect? box) {
     return PdfAnnot(
@@ -82,6 +93,8 @@ class AnnotationLink extends AnnotationBuilder {
         rect: context.localToGlobal(box!),
         dest: destination,
       ),
+      objser: replaces?.ser,
+      objgen: replaces?.gen ?? 0,
     );
   }
 }
@@ -92,6 +105,7 @@ class AnnotationUrl extends AnnotationBuilder {
     this.date,
     this.subject,
     this.author,
+    this.replaces,
   });
 
   final String destination;
@@ -102,6 +116,8 @@ class AnnotationUrl extends AnnotationBuilder {
 
   final String? subject;
 
+  final PdfIndirect? replaces;
+
   @override
   PdfAnnot build(Context context, PdfRect? box) {
     return PdfAnnot(
@@ -113,6 +129,8 @@ class AnnotationUrl extends AnnotationBuilder {
         author: author,
         subject: subject,
       ),
+      objser: replaces?.ser,
+      objgen: replaces?.gen ?? 0,
     );
   }
 }
@@ -126,6 +144,7 @@ class AnnotationSquare extends AnnotationBuilder {
     this.date,
     this.subject,
     this.content,
+    this.replaces,
   });
 
   final PdfColor? color;
@@ -142,6 +161,8 @@ class AnnotationSquare extends AnnotationBuilder {
 
   final String? content;
 
+  final PdfIndirect? replaces;
+
   @override
   PdfAnnot build(Context context, PdfRect? box) {
     return PdfAnnot(
@@ -155,6 +176,8 @@ class AnnotationSquare extends AnnotationBuilder {
         author: author,
         subject: subject,
       ),
+      objser: replaces?.ser,
+      objgen: replaces?.gen ?? 0,
     );
   }
 }
@@ -168,6 +191,7 @@ class AnnotationCircle extends AnnotationBuilder {
     this.date,
     this.subject,
     this.content,
+    this.replaces,
   });
 
   final PdfColor? color;
@@ -184,6 +208,8 @@ class AnnotationCircle extends AnnotationBuilder {
 
   final String? content;
 
+  final PdfIndirect? replaces;
+
   @override
   PdfAnnot build(Context context, PdfRect? box) {
     return PdfAnnot(
@@ -197,6 +223,8 @@ class AnnotationCircle extends AnnotationBuilder {
         author: author,
         subject: subject,
       ),
+      objser: replaces?.ser,
+      objgen: replaces?.gen ?? 0,
     );
   }
 }
@@ -211,6 +239,7 @@ class AnnotationPolygon extends AnnotationBuilder {
     this.date,
     this.subject,
     this.content,
+    this.replaces,
   });
 
   final List<PdfPoint> points;
@@ -229,6 +258,8 @@ class AnnotationPolygon extends AnnotationBuilder {
 
   final String? content;
 
+  final PdfIndirect? replaces;
+
   @override
   PdfAnnot build(Context context, PdfRect? box) {
     final globalPoints =
@@ -254,7 +285,12 @@ class AnnotationPolygon extends AnnotationBuilder {
       subject: subject,
     );
 
-    return PdfAnnot(context.page, pdfAnnotPolygon);
+    return PdfAnnot(
+      context.page,
+      pdfAnnotPolygon,
+      objser: replaces?.ser,
+      objgen: replaces?.gen ?? 0,
+    );
   }
 }
 
@@ -267,6 +303,7 @@ class AnnotationInk extends AnnotationBuilder {
     this.date,
     this.subject,
     this.content,
+    this.replaces,
   });
 
   final List<List<PdfPoint>> points;
@@ -283,6 +320,8 @@ class AnnotationInk extends AnnotationBuilder {
 
   final String? content;
 
+  final PdfIndirect? replaces;
+
   @override
   PdfAnnot build(Context context, PdfRect? box) {
     final globalPoints = points
@@ -313,7 +352,12 @@ class AnnotationInk extends AnnotationBuilder {
       content: content,
     );
 
-    return PdfAnnot(context.page, pdfAnnotInk);
+    return PdfAnnot(
+      context.page,
+      pdfAnnotInk,
+      objser: replaces?.ser,
+      objgen: replaces?.gen ?? 0,
+    );
   }
 }
 
@@ -335,6 +379,7 @@ class AnnotationTextField extends AnnotationBuilder {
     this.value,
     this.defaultValue,
     this.textStyle,
+    this.replaces,
   });
 
   final String? name;
@@ -369,6 +414,8 @@ class AnnotationTextField extends AnnotationBuilder {
 
   final String? subject;
 
+  final PdfIndirect? replaces;
+
   @override
   PdfAnnot build(Context context, PdfRect? box) {
     final _textStyle = Theme.of(context).defaultTextStyle.merge(textStyle);
@@ -396,6 +443,8 @@ class AnnotationTextField extends AnnotationBuilder {
         fontSize: _textStyle.fontSize!,
         textColor: _textStyle.color!,
       ),
+      objser: replaces?.ser,
+      objgen: replaces?.gen ?? 0,
     );
   }
 }

@@ -20,6 +20,7 @@ import 'dart:typed_data';
 import 'package:vector_math/vector_math_64.dart';
 
 import '../../pdf.dart';
+import '../pdf/format/indirect.dart';
 import 'basic.dart';
 import 'border_radius.dart';
 import 'box_border.dart';
@@ -89,6 +90,7 @@ class ChoiceField extends StatelessWidget with AnnotationAppearance {
     required this.name,
     required this.items,
     this.value,
+    this.replaces,
   });
   final String name;
   final TextStyle? textStyle;
@@ -96,6 +98,7 @@ class ChoiceField extends StatelessWidget with AnnotationAppearance {
   final double height;
   final List<String> items;
   final String? value;
+  final PdfIndirect? replaces;
 
   @override
   void paint(Context context) {
@@ -125,7 +128,12 @@ class ChoiceField extends StatelessWidget with AnnotationAppearance {
       );
     }
 
-    PdfAnnot(context.page, bf);
+    PdfAnnot(
+      context.page,
+      bf,
+      objser: replaces?.ser,
+      objgen: replaces?.gen ?? 0,
+    );
   }
 
   @override
@@ -144,6 +152,7 @@ class Checkbox extends SingleChildWidget with AnnotationAppearance {
     double width = 13,
     double height = 13,
     BoxDecoration? decoration,
+    this.replaces,
   })  : radius = decoration?.shape == BoxShape.circle
             ? Radius.circular(math.max(height, width) / 2)
             : decoration?.borderRadius?.uniform ?? Radius.zero,
@@ -171,6 +180,8 @@ class Checkbox extends SingleChildWidget with AnnotationAppearance {
 
   final Radius radius;
 
+  final PdfIndirect? replaces;
+
   @override
   void paint(Context context) {
     super.paint(context);
@@ -217,7 +228,12 @@ class Checkbox extends SingleChildWidget with AnnotationAppearance {
       child!,
     );
 
-    PdfAnnot(context.page, bf);
+    PdfAnnot(
+      context.page,
+      bf,
+      objser: replaces?.ser,
+      objgen: replaces?.gen ?? 0,
+    );
   }
 }
 
@@ -232,6 +248,7 @@ class FlatButton extends SingleChildWidget with AnnotationAppearance {
     this.flags,
     required Widget child,
     required this.name,
+    this.replaces,
   })  : _childDown = Container(
           child: DefaultTextStyle(
             style: TextStyle(color: textColor),
@@ -282,6 +299,8 @@ class FlatButton extends SingleChildWidget with AnnotationAppearance {
 
   final Set<PdfAnnotFlags>? flags;
 
+  final PdfIndirect? replaces;
+
   @override
   void paint(Context context) {
     super.paint(context);
@@ -300,7 +319,12 @@ class FlatButton extends SingleChildWidget with AnnotationAppearance {
     drawAppearance(context, bf, mat, _childRollover,
         type: PdfAnnotAppearance.rollover);
 
-    PdfAnnot(context.page, bf);
+    PdfAnnot(
+      context.page,
+      bf,
+      objser: replaces?.ser,
+      objgen: replaces?.gen ?? 0,
+    );
   }
 }
 
@@ -323,6 +347,7 @@ class TextField extends StatelessWidget with AnnotationAppearance {
     this.value,
     this.defaultValue,
     this.textStyle,
+    this.replaces,
   });
 
   final Widget? child;
@@ -342,6 +367,7 @@ class TextField extends StatelessWidget with AnnotationAppearance {
   final String? value;
   final String? defaultValue;
   final TextStyle? textStyle;
+  final PdfIndirect? replaces;
 
   @override
   Widget build(Context context) {
@@ -386,7 +412,12 @@ class TextField extends StatelessWidget with AnnotationAppearance {
       );
     }
 
-    PdfAnnot(context.page, tf);
+    PdfAnnot(
+      context.page,
+      tf,
+      objser: replaces?.ser,
+      objgen: replaces?.gen ?? 0,
+    );
   }
 }
 
@@ -405,6 +436,7 @@ class Signature extends SingleChildWidget with AnnotationAppearance {
     this.crl,
     this.cert,
     this.ocsp,
+    this.replaces,
   })  : value = value ?? crypto,
         super(child: child);
 
@@ -440,6 +472,8 @@ class Signature extends SingleChildWidget with AnnotationAppearance {
   /// Online Certificate Status Protocol
   final List<Uint8List>? ocsp;
 
+  final PdfIndirect? replaces;
+
   @override
   void paint(Context context) {
     super.paint(context);
@@ -475,6 +509,11 @@ class Signature extends SingleChildWidget with AnnotationAppearance {
       drawAppearance(context, bf, mat, child!);
     }
 
-    PdfAnnot(context.page, bf);
+    PdfAnnot(
+      context.page,
+      bf,
+      objser: replaces?.ser,
+      objgen: replaces?.gen ?? 0,
+    );
   }
 }