SECURE E-BOOK

Hello I will soon be selling a PDF e-book on the Internet through ClickBank. I need someone who can implement some kind of security so that when people buy the book and it goes to the "thankyou" page for download, people cant just type the URL in and download it without paying. This is a simple task for the right person as ClickBank already have some kind of instructions for this although I am not good with this kind of thing. Also, I know that there is software on the net that ensures people cant send the ebook to anyone else as it has some kind of licence security built in - anyone know how to do that? This is urgent plese respond if you can do this and quickly. Thank you. Rakesh