Well, the end goal in this is to do as much as we can to protect our products from theft... if a password is required to open the file, and it is unique for each order, at least there's some effort involved if someone wants to copy the materials (they'll have to give the password to others as well.) I've done this in the past with other pdf materials, and it's about the only way that I know of to at least somewhat protect our materials.

I know that I need to modify the code - that's why I'm asking WHICH php files are involved, so that I can speed up my modification process. (The last time I did this was with a site using VirtueMart, same idea but running under Joomla, so I've been through this before.)

I'm not a complete rookie, just a rookie as far as Zen Cart is concerned. I DO have the skills required to make the modifications. I just thought I'd ask to give myself a jump on the process - gotta start somewhere. So thanks for your help. Now, if we can skip the pontification and attitude, if someone can help me by just pointing me to which files are involved, I'll take it from there. If not, I'm sure I can figure it out.