Yes. You need someone to follow the trail of a pdf and find out what is getting messed with.
Someone that knows about the beast Exchange. things to check are encoding setups all the way through, and clients as well.
check your receive / send connectors. make sure these setting are all checked and set appropriately.
check the header for what the encoding is:
Content-Transfer-Encoding: uuencode
Content-Transfer-Encoding: base64
make sure there is nothing there out of place.
You have applied all patches/updates to exchange, the OS's and the clients, as well as the security software?
one issue I encountered was related to base64 decoding, and it was the Outlook clients corrupting while decoding the attachment. it would get to a CR and start filling the .pdf with blanks, or truncate file right there. have a look in a hex editor at one of the corrupted files. Cant remember which versions it was though.
I am leaning against it being anything to do with the sec software, and toss-up between, the outlook client, second a dodgy setup somewhere.
Really really hard to figure these out without just sitting down at a console and going through it.
good luck