There is no virus. Your work proxy transparently scans all files going through, and for some reason chokes on that PDF. Rather than let a file go through unchecked, it blocks it.
Here's another fun exercise: access some SSL-encrypted page, and check the certificate chain. I bet your employer is sneakily doing a man-in-the-middle attack on your encrypted connections, without having told you, and gets away with it because he can pre-install his own certificates on your work computer so you don't notice.