I've been doing some head banging on this one and solicit your advice.

I am building an app that as part of it's features is to present PDF forms; meaning display them, allow fields to be changed and save the modified PDF file back out. UIWebViews do not support PDF interactive forms.

Using the CGPDF apis (and benefit from other questions posted here and elsewhere), I can certainly present the PDF (without the form fields/widgets), scan and find the fields in the document, figure out where on the screen to draw something and make them interactive.

What I can't seem to figure out is how to change the CGPDFDictionary objects and write them back out to a file. One could use the CGPDF Apis to create a new PDF document from whole cloth, but how do you use it to modify an existing file?

Should I be looking elsewhere such as 3rd party PDF libs like PoDoFo or libHaru?

I'd love to hear from anyone who has successfully modified a PDF and written it back out as to your approach. Thanks!