Please can someone also explain to me how you can ensure that my Word files are never converted into LibreOffice files again.
Possibly Do you save wrong.
I suspect that they do not actually convert, but that LibreOffice (new?) Has been installed and registered as the default program for this file type. That can be changed: https://support.microsoft.com/...0a32e1894d
Did you choose Open Document Format (ODF) when you set up Word?
And what format do you use when saving Word documents?