As far as i know, Just by Copy-Paste. Of course any browser and OS, and word program, you can choose to either Select-All, COPY, and then Paste As Plain Text or paste as Styled text or HTML. You would have to go thread-by-thread. Unless you configure a 3rd party web crawler to collect your forums. In conclusion YES roll20 has a way to Backup (make a Roll20 copy) of your entire game, and that backup feature can optionally include your Game Forums, but it is not an EXPORT.
