save and restore Annotation in flutter (syncfusion_flutter_pdfviewer)

I'm using syncfusion_flutter_pdfviewer: ^30.2.7 I'm adding annotation with builtin toolbox now I want to save the information of the annotation somewhere, so I could add them automatically when pdf opened next time but Annotation class does not return any information about added annotation, and adding annotation using controller is really messy

SfPdfViewer.asset(
            "lib/assets/sample.pdf",
            controller: c.controller,
            undoController: c.undoController,
            scrollDirection: PdfScrollDirection.vertical,
            interactionMode: c.panMode.value ? PdfInteractionMode.pan : PdfInteractionMode.selection,
            pageSpacing: 20,
            onPageChanged: (PdfPageChangedDetails details) => c.pageNumber(details.newPageNumber),
            onTextSelectionChanged: (PdfTextSelectionChangedDetails details) {
              c.selectedText.value = details.selectedText ?? "";
            },
            onAnnotationAdded: (Annotation annotation) {
              annotation.color = c.selectedColor.value;
              UAnnotationType type = UAnnotationType.highlight;
              if (annotation is UnderlineAnnotation) {
                type = UAnnotationType.underline;
              }
              if (annotation is HighlightAnnotation) {
                type = UAnnotationType.highlight;
              }
              if (annotation is SquigglyAnnotation) {
                type = UAnnotationType.squiggly;
              }
              if (annotation is StrikethroughAnnotation) {
                type = UAnnotationType.strikeout;
              }
              if (annotation is StickyNoteAnnotation) {
                type = UAnnotationType.stickyNote;
              }
              c.addAnnotation(
                UAnnotation(
                  type: type,
                  pageNumber: annotation.pageNumber,
                  color: c.selectedColor.value,
                  text: c.selectedText.value,
                ),
              );
            },
            onAnnotationDeselected: (Annotation annotation) {},
            onAnnotationEdited: (Annotation annotation) {},
            onAnnotationRemoved: (Annotation annotation) {},
            onAnnotationSelected: (Annotation annotation) {},
            onTap: (PdfGestureDetails details) {
              if (c.addNoteMode.value) {
                c.addStickyNote(details.pagePosition);
              }
            },
          )

class UAnnotation {
  final String id = UUUID.uuidV7();
  final UAnnotationType type;
  final Color color;
  final int pageNumber;
  final String text;

  UAnnotation({
    required this.type,
    required this.pageNumber,
    required this.color,
    required this.text,
  });
}