Sorry I was not too clean, my (quite hacked) PW2 is now used by my wife and I changed to Aura HD, so I definitely need the Kobo things. I think during the weekend I decide what I would like to do. My problem in more detail is that the simple usage of Koreader is only on the kindle side (opening PDF from the library opens by default koreader, on long press stock reader can also be selected). I understood on Kobos i have to start koreader file manager first, and it requires more efforts then I first thought
.
(And thank you for your efforts in spite of my stupid questions.)