If you've got multiple articles and several PDF documents available, make sure you've got one page on your web site that lists all of this affiliate program information and makes it easily accessible. Consider adding a link on your home page that can direct rushed visitors to this page (this type of simple efficiency will draw visitors back to your site). When you provide quality information on your affiliate site though ebooks, consider the viral aspect. People might share this information with friends, family, or coworkers who will potentially visit your site as well.
The cost of the original document creation is a small price to pay for the potential exposure you may receive. Making printable information available is a great way to start a chain reaction that can get your site noticed.