The WP PDF Stamper plugin allows you to dynamically stamp a PDF file with the customer’s details (example: name, email, address etc.) upon purchase. The PDF stamper then sends the stamped copy of the PDF file (your eBook) to the customer via email.?
This has the major advantage of discouraging people from sharing your e-books illegally.
Additionally, you can password protect the stamped PDF files with the customer’s email address and encrypt the PDF files to prevent users from being able to copy, modify or print the content of the file.