many users report that they are unable to transfer ebooks from Adobe Digital Editions 4.5 to compatible e-readers (like Kobo and many others)
all these issues happen with ebooks provided in epub3 format and protected with Adobe DRM
these ebooks usually open correctly on computers with ADE 4.5, but when you try to copy them to your e-reader you get an error message saying "your ereader is not authorized to open this book”; the ebook cover appears all black on the e-reader and you cannot open it
the only solution, at the moment, is for the user to install a 3.0 version of ADE
this fallback solution seems to work for everyone but Mac users who have a very recent OS version (from Catalina onwards they don’t support ADE 3.0 anymore)
NB. the problem here described happens only with loans: the same ebooks in the same format - when they are provided for a standard sale with no time limits - can be regularly copied on a compatible e-reader through ADE 4.5. So the problem seem to happen only in ebooks protected with time adobe drm
I am having this EXACT problem. I've done hours of internet research to try and find a solution. I've spoken with Kobo who can't provide a solution and spoken to several Adobe chat people who have no answer. So frustrating!!!