AnnotationsApi.exportXFDF()

The annotations and the form field values as XFDF — the interchange format Acrobat, Nutrient and Apryse read. Every text mark, note, shape, drawing, polygon, free text and stamp with its name, author, subject, dates, color, opacity, flags, contents, pop-up and geometry; replies (inreplyto) and review statuses (state); the fields' values (<fields>, nested by the dots in their names) as doc.forms.getValues() reads them. A stamp goes out by its name and box alone — its picture stays in the document; a member of an annotation group goes out as an annotation of its own. Dates go out as PDF date strings, coordinates are the page's own, colors #RRGGBB.

Names are the hinge: the SDK writes every annotation's own name as its name, matches by it on import, and reads Acrobat's own names back, so a round trip through a review backend neither duplicates nor loses a comment. Needs the extract feature (the file carries the document's words) and, for the annotations, annotations.