An update to date version of DeDRM and the KFX Input plugin should be pretty much all you need in addition to the basic calibre install.
I would suggest using the
10.0.9 version and the latest KFX Input plugin. You can check in the Plugins segment of calibre's preferences to see what versions you currently have installed. If you are feeling a bit enthused, you can try the alpha release of DeDRM from the links at
Automatic alpha release with latest changes.
If you still have issues with conversion, then you may want to post in the
KFX Input plugin thread.