According to the answer of a/4047420/1875208
Little bit late but this one works only with commandline-execution, such as exec();
You need at least provide 3 parameters:
Path to rtf2htm on your server
Path of the rtf-document (yes, youÃ‚Â´ll need to save it to a file
Filepath to where the converted html should be outputted.
It could then look like this:
exec(rtf2htm file.rtf file.html);