|
From your description it seems they are epub files, which is one of the main ebook standards these days. However, which DRM or encryption scheme they use, is not obvious. It could be Adobe epub DRM (most probable) but could also be a more exotic one. You should perhaps ask the person who gave you the device about the origin of these files. If you know where they were bought or acquired, it would be easy to identify the encryption method.
|