Hello,
Setting autoUpdate to true enables an internal option in the DOCX to request the DOCX reader to update the TOC when the document is opened (OOXML standard). MS Word shows a dialog to update the TOC if the user accepts it, but this option is only supported by MS Word; other programs such as LibreOffice or Google Docs don't support it, so it needs to be updated manually (LibreOffice also supports using a macro to update it).
Using the conversion plugin based on LibreOffice you can update TOC contents in DOCX files.
Regards.