Hello,
We've recently run into this error message when certain users are trying to open PDF's from our repository. We haven't made any major changes to the repository or permissions that I'm aware of, the only change in our environment is switching to Foxit PDF Editor for some users. I'm able to open the files in question from one of our user complaints, so I'm not entirely sure where the issue could lie. Unsure if anyone has seen this similar behavior, but I've read a few posts that indicated issues showing up with Adobe as well so I don't think the change in PDF editor is contributing. We've also attempted the fix listed in this post Unable to display the electronic file type for this document - Laserfiche Answers to no avail.