Hello,
Please note that the native conversion plugin supports a set of contents and styles detailed at https://www.phpdocx.com/documentation/conversion-plugin/preparing-the-templates-for-its-conversion (Supported OOXML tags and attributes when using the native method section).
If the DOCX to be transformed uses contents and styles not supported by the native conversion plugin, it's recommended/required to use the conversion plugin based on LibreOffice to get a proper output, as advised on the documentation pages (https://www.phpdocx.com/documentation/conversion-plugin/information Which method to use for the conversion? section). The conversion plugin based on MS Word can also be used.
Regards.