I am still confused: Conversion IS part of Calibre. Or are you using the KFX plugins to up convert?
There are OLDER plugins that are not maintained that will no longer work with newer Calibre Major versions. Preferences:getplugins: (select installed at the top to see if what you have installed): The Calibre column list the required version to run
There are links to the No DRM site on MR (that is allowed, so here you are)
https://github.com/noDRM/DeDRM_tools/releases