EDIT: AnemicOak was quickly than me. Thank you!
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I haven't played with library books, yet.
Library books are usually ePub or pdf. You can't have both epub and pdf library books on your Reader at the same time. Right now, they don't play well together. Both are usually DRM'd ( ADE epub and ADE pdf).
I have downloaded DRM'd freebies.
I seem to remember something I chose was open in ADE. Either way I got it in ADE and loaded it to my Reader.
I hope someone who has experience with this will jump in. I know how frustrating it can be trying to figure this stuff out.