I have a PDF version 1.5 here which I started commenting on with Foxit Reader 4. If I open the commented PDF in Adobe Reader 9 now, I get the following message:
This document enabled extended features in Adobe Reader. The document has been changed since it was created and use of extended features is no longer available. Please contact the author for the original version of this document.
The document properties in Adobe Reader say that the document is not allowed to be commented.
How can I prevent this and keep the document commentable in both Foxit and Adobe Reader?
Best Answer
Update as of February 2013
According to this answer Adobe Reader XI removed the restrictions I mentioned before.
My old answer:
I think this is not possible at all. Adobe uses a private digital signature inside the documents they mark as "annotation enabled". Once you modify this document with a third party software as Foxit Reader, Amyuni PDF Creator, etc the digital signature is not longer valid. It is not possible at the moment for third party software to produce this signature.