You can encrypt PDF with certificate encryption. During the encryption process you create a list of possible recipients by including their public key certificates. Then only recipients that have one of the corresponding certificates with a private key installed on their computer will be able to open this PDF.
The problem with this approach is that each of the potential recipients of your PDFs must have an encryption certificate with a private key and send you the same certificates but with public key only.
Thanks, Im gonig to look into this... Im not sure it will do exactly what Im hoping but it's certainly a step in the right direction. Thanks!