Both .harx and .cmtx files originate in e-Sword bible study software, but it does not look like you can convert one to another or vice versa. But maybe there is some way to export some data or something like that, we couldn't find any references about this on internet though.
Convert e-sword harmony file to e-Sword commentary data.
We found one software available in the database for this conversion.
Microsoft Windows software - convert harx to cmtx on Windows
Bible study computer software
Convert from harx 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.