The important key there bein' "DRM-free" … The file format (epup, pdf, plaintext, whatever) doesn't matter quite as much as that particular detail, as long as t

The important key there bein' "DRM-free" … The file format (epup, pdf, plaintext, whatever) doesn't matter quite as much as that particular detail, as long as the file format is one that doesn't require a proprietary reader. If I can't buy a book in a lasting and reliable (cross-platform-friendly) file format, then I'm not buyin' it. (Your choice of epub is certainly an especially good option to go with in that regard.)