If someone really wants to copy it, they will. Even if it's the newest and most secure uncrackable DRM method, someone can print screen it, OCR it, style it and make a very close replica. Print screen is easier (and faster) than scanning a paper book. Granted, there aren't many people capable of doing this, but it only takes one.
He/she uploads it to a public torrent tracker and if the book is worth it, it will spread like wild fire. Of course, if the book is worth it, a lot more people will buy it than steal it. So worrying about DRM is counter productive, in my opinion. You should be worrying about the content instead.