I was chatting with my boss this morning and showing the Digusign system working, we figured out that if the process was automatic then it would be a very useful service.

We use a program called A-PDF Server to automatically add a header and footer to any PDF saved onto a particular directory on the server, ideally after this process is complete another program would create a hash of the pdf and save a text file (of the same filename) which has the hash + transaction number + instructions how to verify that the pdf has not been modified, then process a payment taken from a pre-filled wallet.

www.a-pdf.com    possibly a collaboration with this company could be easier than creating another piece of software.