The page we linked above also mentions at the end some third-party eBook "compiler" solutions we're aware of, with instructions on integrating them with E-junkie; however, these usually work by converting your eBook into a Windows-specific executable program file, so this would exclude Mac users from your potential buyer demographic.
Our PDF Stamping feature is a rather strong deterrent to file sharing, since every copy would contain the name and email address of the buyer who originally shared-out the copy they'd purchased and downloaded from you, along with the unique Transaction ID of their checkout payment. Their name and email are typically taken from their payment account profile (e.g. their PayPal email and registered account holder's name), so this would be hard to populate with bogus data.
We discuss some additional points regarding file -sharing and -locking on this FAQ page:
http://www.e-junkie.com/ej/faq.ebook.security-tradeoffs.htm
