Hi, my sister got a transformer tablet TF 101. She has a lot of epub files on her computer that she wants to put on her tablet, she has a kindle app and Nook app. I can convert the files to pdf, but that doesn't work. When I try to copy and paste the file into the nook or kindle folder, the error message comes up saying that the file is not compatible. Is there a file type I can convert these books to? Or is the only way for her to read books on her tablet is to buy them straight from her tablet?