Hello,
If you need to do parallel conversions in the same OS, then killing the MS Word process is not a proper solution because Windows may use a single PID for MS Word (all DOCX documents opened with MS Word may use the same PID, not a single PID for each document).
In this case, it's a good test trying another MS Word version (maybe some version with a valid license that doesn't require an online checking).
Regards.