I'm not familiar with the Denver reader and that would make me afraid to buy it unless I knew something more about it.
If you want to read books from Amazon you can use a Kindle or you can remove the DRM, which we can't really discuss in this or most forums, and use most ereaders.
For reading PDF's some e-ink readers are better than others but I've read that most aren't much good at PDF. I don't read PDF so I don't really have much experience with that. I think most people suggest tablets for PDF files.
The two major brands in ereaders these days are Kindle and Kobo. I have both and I prefer the Kindle but they're both excellent so my preference is more personal than for any real reason. If I only had a Kobo that would be okay too, although if I only had one I'd rather it was my Kindle Voyage.
Formats, once DRM is removed, aren't really much of an issue these days because of Calibre, a freeware program that makes converting between formats trivial.
Barry
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