However, not all is lost. You can use the open source e-book management software Calibre to convert them to EPUB format ...

A new, non-destructive Kindle Jailbreak even works on my 2014 Kindle Voyage. I'm just not sure I needed it. When I saw this ...

The only format Kindle now supports is KFX ... Send to Kinde is something most users don’t use, but it allows you to send EPUB, PDF files, or other comic formats to your Kindle.