Doing DRM right is hard. I know you don't want to hear this, but this is central to the issue. Make it not strong enough and you might as well not have bothered, too strong and you make your product too hard to use. It is not clear at all that there is a middle point between these two that satisfies them both.
How it is usually done: buy it. Here is one reason to buy it, beyond the obvious "it is fast and easy", the ereader that you use must know how to interpret the drm. So if you build the DRM you have to build the reader software. And get it on devices. Still with me? Now, where are the directions? Well, you are asking companies that makes stuff to keep content restricted to tell you how their code works? Patented is how. Open source drm is kind of a contradiction in terms (actually see here). Creating drm is a big project even for a big developer, as far as I can tell. The sensible thing to do is sell through something like the Amazon Kindle market.
Here is an article on why not DRM that seems ok
http://www.learnoutloud.com/content/blog/archives/2006/11/the_top_10_argu.html
Maybe look in to watermarking? You might be able watermark a serial number in to the file. That would make it easier to tell where copies are coming from at least.
How it is usually done: buy it. Here is one reason to buy it, beyond the obvious "it is fast and easy", the ereader that you use must know how to interpret the drm. So if you build the DRM you have to build the reader software. And get it on devices. Still with me? Now, where are the directions? Well, you are asking companies that makes stuff to keep content restricted to tell you how their code works? Patented is how. Open source drm is kind of a contradiction in terms (actually see here). Creating drm is a big project even for a big developer, as far as I can tell. The sensible thing to do is sell through something like the Amazon Kindle market.
Here is an article on why not DRM that seems ok
http://www.learnoutloud.com/content/blog/archives/2006/11/the_top_10_argu.html
Maybe look in to watermarking? You might be able watermark a serial number in to the file. That would make it easier to tell where copies are coming from at least.