I've never heard about a PDF file being currupted as a result of being scanned by FOPE, but there is a first time for everything :)
If you really thing that the issue is created by FOPE and not by the PDF reader on the receiving end I will recommend that you give MIcrosoft Fope support a call.
Your can find the contact information at this download link: http://www.microsoft.com/download/en/details.aspx?id=28774
A good way to test if the PDF have been currepted during the FOPE processing would be to send the file back to the sender and get them to verify they can't read the file
Hope you solve your issue.
Peter Selch Dahl - www.peterdahl.net - Blog: http://blog.peterdahl.net - Twitter @PeterSelchDahl
I think it is not FOPE which have tampered the attachment. Please update me the Configuration of the Inbound Mail flow and the Components involved in Mail Delivery for your domain where you received that attachment.
I would also like to know which subscription have you subscribed for FOPE (BPOS, Office 365 or FOPE for Onpremise Mailing Solutions).
I would also like to know was there notification sent you by Microsoft or Forefront regarding this action taken on that PDF file?
------- Pradeep Samant (FOPE ROCKS!!!)