It's a bad PDF. Are they all from the same source?
There is a base file that we make a copy of each day and multiple users work on the copy back and forth.
Thing is, sometimes the corruption happens and sometimes it doesn't. Making the the base file not as
consistent as the issue. Do you think the copy is randomly getting corrupted as people edit and save it?
I think that's likely. There is a lot of PDF software from different vendors (including each browser maker) so it may be worth trying to find a pattern in the software used. It's also possible that the file is damaged somehow, especially if it is emailed where this becomes very likely.
The files are worked with in a shared folder through our internal network/terminal server connections and the tools used to edit and save it are Adobe Acrobat 9 (IX) and 11 (XI) Pro if that information helps.
This is an awkward one, I realise. Your users will want to just get on. One possibility is that two people have the file open for editing: depends if the file locking works.
One one thing to try is Acrobat Pro's preflight looking for validating the PDF. For syntax errors.
Have you got a pattern in particular users being more likely to corrupt the file?