Hundebub, listen to what darryl and the others have said about converting to azw3.
The converting process is more or less merely replacing the wrapper. The internals of all of these different formats is html, the same stuff that's used for web pages. So you don't have to worry about degrading them or losing information.
See this page for what happens during a conversion:
https://manual.calibre-ebook.com/conversion.html