There is the key phrase… in their own app. You would need the application that knows how to export its unique internal document format into PDF to do this for you using a Run AppleScript, and the specific AppleScript Dictionary terms that tell that application how to export the PDF. You cannot convert these documents to PDF without the controlling application involvement.
LibreOffice has a command-line soffice tool that can convert from one supported document format to another (e.g. Word or Excel to PDF. This could be used in an Automator Quick Action comprised of a Run Shell Script action.