[rsbrux]

I am trying to migrate my eBooks from an old Sony Pocket Edition to a new Onyx Boox Poke 3. I am running Calibre 5.14 under Windows 10 Pro x64 20H2. I have installed the Apprentice DeDRM v7.2.1 plugin in Calibre and have tried loading the library directly from the PRS-300 as well as from a backup of my previous Calibre library. In both cases, the books with DRM are unreadable in Calibre and on the Poke 3, although I can still read them on the PRS-300.
The DeDRM instructions say to use "File - Import" in Calibre, but I did not find any "Import" command in the Calibre UI, so I used the "Add to library" command instead. The DeDRM instructions also call for "the original downloaded ebook files", but I don't think I have any such thing. My PC is running a "bare metal" Windows 10 installation, and the only files I could find were a backup I made of my previous Calibre library directory before (re-)installing Windows.
The books were originally purchased on various bookstore sites, including but not limited to Amazon. It would be quite difficult for me to reconstruct which books came from which vendors. Since I can still read the books on the Sony, I was hoping that importing them directly from the reader would provide whatever key is needed to unencrypt them.
I haven't used it in several years, but my Adobe login still works. However, I don't find any information about licensed books in my Adobe profile.
Is there any hope of migrating the DRM-protected books?