When I click this button:
I get this:
Yes, we forbid exports on xwiki.org to avoid DDOS attacks 
(exports take a lot of CPU/resources). This check is done at the level of the web server (front end to xwiki) and is not a feature of XWiki (hence why the button is there in the UI).
Well, then FYI, the PDF export does work. 
hmm that’s weird, normally the /export/ action is forbidden Maybe we allowed PDF export, I don’t recall.