I need to apply password/encryption to several thousand PDFs in a scheduled batch process

My situation is as follows:

We generate PDFs out of Optio in a nightly process and send those PDFs out via email to their respective addresses through another scheduled process.  We now need to encrypt and password protect those PDFs prior to being emailed via a scheduled process.  The passwords are unique and stored in a MySQL database.  I have read conflicting posts here and there saying that it can/cannot be done.  Figured I would post here and let the experts weigh in.

thanks all.