I'm writting a ebook and I'm gonna to sell it soon.

I'd sell it at Google Play Store, but here in Brazil they don't accept PayPal as payment (and many brazilian don't have a credit card), so I think that the best option is to sell it by myself.

I could sell it also at Amazon, but the Kindle format just sucks when you work with (a lot of) equations.

But, of course, there's a problem about sending the pdf file to the buyer. My friend suggested me to lock it with a serial key - like a software. Then a person could open it just in one or three computers. I know there's a package that lock the pdf file with a password (that I create), but I'd like to have a way that block this password when it's used a lot of times - really like a software.

Is it possible?

Do you have any other ideas to protect a pdf file?

I'm gonna take the copyright of my ebook here in Brazil and I know that I can't protect it totally, but I'm trying to do everything I can do to protect it.

There's also a brazilian site (www.hotmart.com.br) where you can publish anything you want and they say that, about pdf files, they print in each page the document number of that one who bought my ebook.

Thanks! :)


For the kind of protection, that you want, you need a Digital Rights Management (DRM) scheme. Unfortunately, those are kind of inconvenient, expensive, or both. Also, most commercially available schemes are either broken or can be worked around.

For example if you want to count how many computers are used to open a specific copy of your e-book, those computers need to contact a server of yours. That's inconvenient for your customers, who have to be online to read your book. The will probably be limited to a certain software reader. And they have to be okay with the fact that you can track their reading behaviour. Also, when some time in the future you decide that you do not longer want to maintain the server, they might not be able to read the book any longer.

You can ask a publisher to sort the details out for you -- Amazon is not the only one offering that kind of service. That will free you of the burden to run a DRM-Server, and probably will give your customers a larger degree of compatibility as well.

If you expect to have a limited audience, a Traitor Capturing Scheme like the one mentioned in your last paragraph might be a better idea: You can for example compile a personal edition of your e-book, with the name of your customer (if it's a present, the presentee's Name) and a short text explaining that it's pretty uncool to copy this book. Watermarking, encrypting or digitally signing might be a good idea to make sure, the name stays there.

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