Originally Posted by dwanthny
He's not disagreeing with this theory. He is however saying that the process calibre uses to add metadata causes this pdf file to be changed in such a way that even Adobe acrobat is no longer able to open the full file.
Yes, that's exactly right.
I'm happy to test the portfolio theory and report back. How can I tell if my PDF is a portfolio, and how can I convert the portfolio to a flat PDF? I'm on Windows and Linux. Alternatively, I can send the possibly-portfolio PDF to whoever wants to investigate it.