[Quoth]

See can LO Writer open your Wordperfect files, and what formats WP can save/export in.

Which Wordperfect is it?

Edit LO Writer in odt, but an extra Save As in docx for Calibre.

Switch to LO Writer. Wordperfect for Windows was dead twenty years to thirty years ago. Wordperfect for DOS dead 35 years ago.

Edit:
LO Writer certainly opens some versions of Wordperfect directly.
It's free and runs on Mac, Windows and Linux.