The obvious choice for this conversion would be to use the original software for .mwd documents - Mariner Write. However, it is only available for OS X, so if you do not have access to a Mac computer, you ma have trouble working with this document. It seems the LibreOffice Write supposedly supports at least some version of .mwd documents, so it's worth a shot.
Convert Mariner Write document file to Rich Text Format document.
We have found 2 software records in our database eligible for .mwd to .rtf file format conversion.
Apple macOS / Mac OS X software - convert mwd to rtf on OS X
A word processing program for Mac
Convert from mwd file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned mwd to rtf. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Multiplatform software - convert mwd to rtf on any platform
Full-featured word processing and desktop publishing tool from LibreOffice suite