We noticed that build-in iOS PDF renderer does not support annotations. This means that the email app, Safari (I think) and some other apps simply won't display our standard PDF annotations added with help of PDFNet SDK.
As a workaround we are now flattening annotations (using pdftron.PDF.PDFDoc.FlattenAnnotations()).
As a result, annotations can be viewed even in PDF viewers that do not support annots (such s iOS mail app, aswell as Safari).
Just wanted to know, if there is anyway to un-flatten the annotations – or temporarily flatten the annotations to a PDF using PDFNet SDK?
The main issue is that since we flattened annotations, we are no longer able to see them in Annotation Summary (they are no longer annotations).
When you flatten annotations, they're pretty much lost. There's no way to tell a flattened annotation from regular content.
You could definitely use some tricks such as add custom entries in the form xobject dictionary to distinguish annotation from the rest of the page content, but this could backfire if a user decides to edit PDF with some third party software.
I would suggest that you create a copy of the PDF and flatten that instead of the original if you want to save the original content. This is simply a shortcoming of Apple's preview.