If you are having odd issues with a mail message attachments, before you start tearing the system apart, try rebuilding the mailbox.  Occassionally, I will receive a call complaining that the user can not open a particular PDF with Preview, Acrobat Reader, or quick look.  Yet, the message when forwarded somewhere else opens fine, the trouble was confined to Apple Mail.  The user may even get a message stating the file was corrupt…

Try rebuilding the mailbox on the MacBook Pro. Sure enough, after selecting Mailbox » Rebuild, all the troublesome PDF attachments were magically resolved — previewing and saving both work as expected now. The odd thing about this is that, outside of messages with PDF attachments, that account was working perfectly.