Hello,
Please paste the content of the config/phpdocxconfig.ini file you are using (removing license information).
As you are using a Windows server, also note the following information from the documentation page (https://www.phpdocx.com/documentation/conversion-plugin/common-problems-and-possible-errors):
phpdocx set up file: If the path to LibreOffice in the config/phpdocxconfig.ini file contains spaces, you have to wrap it between single quotation marks, e.g.:
path = '"C:\Program Files (x86)\LibreOffice 5\program\soffice.exe"'
Regards.