Question Downloadable or Admin Uploads

Was hoping I could get some help from some of the more experienced people here about the following question.

1. I need the ability to upload a different pdf file that is private to each order after the order is completed. So I need the ability as the admin of the store, to upload a pdf file and attach it to the customer's order after the order is complete. It will be a different pdf file for each order, so each time even if same customer orders, I'll need to attach a different and unique pdf file to each order for the customer and the pdf should only be accessible and downloadable by that individual customer.

A: Does anyone know of an extension or module, that exists for the admin to accomplish this type of function?

If not, is there one that is "close" so that I could perhaps email the developer and see if possible to do as a customization?

Thanks for your help.