sharepoint online – What are the requirements to retain custom document properties when exporting to PDF

SharePoint colums (metadata) add extra document properties to the Word document.
When I download such a document I can view the extra properties In Word with File>Info>Show All Properties.
When I export the file to PDF with File>Export>Create PDF/XPS, with document properties checked in Options, the extra document properties are not transferred or not visiable in the resulting PDF document.
What are the requirements to retain the custom properties in PDF and show them?
Do I need specific software or specific version, I use the latest version of Office 365 and SharePoint Online.