Submission + - Now available as ebook: The LaTeX Companion 2nd edition
There's no DRM protection, the ebook is just watermarked.
That book is a classic one, now we can see how this LaTeX made book of more than a thousand pages looks in modern ebook formats on iPad, Android tablets, and smartphones.
Until the end of October, there's a promotion price for the the bundle in those three formats — you can get it for just $14.99. Or get a free copy: you can win one at a just launched contest on LaTeX-Community.org, running from Oct 20 to Nov 10, 2013.