I've escalated this issue because FFcore 6.0 can process this kind of PDF files and 6.2 not. This was the answer,
Unfortunately this is working as designed.
The whole point to digitally signing a document is so that you can guarantee it has not been modified since the last signature (ie it is identical to the signed version).
The Devs have had this question before and the response was:
“…Digitally signed PDF docs should not be modified otherwise it invalidates its authenticity. In the case of 2 up and 3up, for example, the document is being modified from it's originally signed content.”
As an FYI a digital signature is in essence a checksum for all the bytes in a PDF (not just a visible signature gif) which is stored internally in the PDF structure. One way you can edit a signed PDF in Acrobat is to “Print to PDF” which then creates a new PDF which does not contain the signature meta data. This then can be modified, but as you can imagine this would be difficult to do programmatically in an application like FFCore.
There are threads on the Adobe communities boards about editing signed PDFs, but they all really end with the comment that you shouldn’t, here are a couple of examples:
https://community.adobe.com/t5/acrobat-discussions/editing-a-signed-pdf/m-p/8794866
https://community.adobe.com/t5/acrobat-discussions/digital-signatures-and-combining-pdfs-in-acrobat-...
So to sum up, FFCore will not modify digitally signed PDFs, as the digital signature indicates that the document should not be modified.
