You can convert using Evernote as an intermediary: https://github.com/zadam/trilium/wiki/Onenote

You’d need to hunt down a copy but there are mirrors since Evernote ended legacy version, and it’d need to be set up in wine to run in linux but it should do the job.

Most services are forced to carry DRM only versions of Ebooks by the book publishers. But there are ways of legally removing the DRM - it’s a faff but doable. I buy epubs and don’t use Kindle (haven’t for a long time) as it’s much harder to remove the DRM and actually own your books.

But way I look at it - if I bought the Kindle version of a book, I can just download a DRM free version by sailing the seas. Fuck Amazon.

DRM-free doesn’t mean piracy. GOGs whole business model is built around selling games DRM free. I don’t pirate but I do use GOG where possible as I hate DRM - it punishes and inconveniences legitimate users for piracy and doesn’t even solve the problem. DRM is just an expensive waste of money for everyone involved.