The link provided above explains how to integrate E-junkie with ClickBank, so once they complete a buyer's checkout payment, we can process that order for you -- i.e., log order details, send emails, stamp PDFs (if you've set that up), and issue download links.
This help page explains how to set up PDF Stamping for your PDF download product:
http://www.e-junkie.com/ej/selling-ebooks.htm