Hello,
Your problem doesn't seem the same than the links you point out. For example on https://www.phpdocx.com/en/forum/default/topic/2067 the PDF was generated correctly but with a default name instead of the custom one.
The error you get is a generic one when the transformation can't be done (https://www.phpdocx.com/documentation/conversion-plugin/common-problems-and-possible-errors). We recommend you to follow the steps explained on https://www.phpdocx.com/documentation/conversion-plugin/debugging-libreoffice to debug it and run the check-conversionplugin.php script included in the package. The first step is testing LibreOffice standalone, then test using PHP CLI and finally using the web server. The most common source of this error is missing rw access for the home folder of the user that runs LibreOffice. Please note that /home may not be the correct home folder of your user, you can get the correct one running:
<?php
echo getenv("HOME");
For further support, please send to contact[phpdocx].com the OS you are using, the version of LibreOffice and the config/phpdocxconfig.ini file of your installation.
Regards.