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 Simple text file.
We have found one software suitable in our database for this conversion.
Apple macOS / Mac OS X software - convert mwd to txt on OS X
A word processing program for Mac
Convert from mwd file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.