Calibre is one of the best ebook tools out there. It's much more than a reader and a library. Calibre even helps you author your own ebooks. In addition to all that, it lets you remove DRM and convert your ebooks between formats. Think of it like a cross between Kodi and Handbrake, but for ebooks.
This is a companion discussion topic for the original entry at https://linuxconfig.org/calibre-drm-removal-for-ebooks-on-linux