I downloaded the book from the community library, cklick-right on the download and choose "open with Adobe Digital Editions". The book appears in my bookcase. (I can now read the book on my laptop)
When I drag the book to the icon of the connected Kobo-reader (left side of the screen), the message "CE_COPY_NOT_ALLOWED" appears.
When I copy the book from my Downloads and paste it in my e-reader a message appears on the e-reader: "This file cannot be openend. It is protected by Adobe DRM and is not accessible with your Adobe ID. Sign in with your authorised Adobe ID and try again."
I have no idea what to do.