Both .ntw and .nwctxt files come from NotheWorthy Composer, with the key difference that .nwt files are from very old version of the software. This most likely means that users searching for ntw to nwctxt conversion are most likely looking for a way to convert older files to new ones.
Unfortunately, we have not found definite answer for this and even .nwctxt files are around for like 15years. So if you face some particular issue, it would be best to contact Noteworthy Composer or to reach out to some online user community for help.