[Zope] How do I encrypt files in the ZODB

I recently finished my first project in Zope! A file managements system with it's own admin screens. I have recently received requirements for the next version in which the client is asking that the contractors have access to everything but the PDFs that have been uploaded. I know that I could encrypt the PDFs before that they are uploaded but the secretaries that do it it have a hard enough time just creating PDFs. This leads me to my subject. How do I encrypt files in the ZODB? With regards to just PDFs. Something in Python? A product that I missed? A How To that I missed? Upload the files to a external file system that is encrypted? Any sugestions, feedback and general ideas are appreciated. Rob G.