As people with the Collector's Book PDF may have noticed, there's a very intrusive Dark Horse watermark on every page, getting in the way of artwork and text. (It's not just GOG's version; the download from the KS backer portal is exactly the same.)

People have managed to edit it out of their copies, but that requires use of a PDF editor: http://forums.obsidian.net/topic/71846-collectors-book-watermark/