Hi there,

If you are still interested into securing your publications there is pretty serious method to control what the end user does with the content he purchased.
For instance you can decide to tie the publication display to a single computer; meaning that the end use could only view it from one and only one computer. He/she can't move it to other device(s) without your knowledge/approval...

It sounds very very restrictive but it efficient.

Here is basically how it works :
1 you purchase a software that will lock (say) your .pdf file and puts in somewhere on a third party server (the vendor of that application you will be using)
2 your customer buys a copy of the book
3 you deliver him with an unlocking code + downloading link
4 he/she opens the book using your code. This will launch a registration process of that Ebook on the secure server.
5 anytime the user opens the book, there will be a verification against the server.

If the user uninstalls/deletes/formats his Os/drive, then the registration will be gone, even if he/she happens to have a backup copy of the file.
You will need to reissue an activation key.

I experienced such a Ebook, 3 times activation reset !!

A link

All the best.