When no or an empty file is produced, the result message from the server will be
{ "result": { "success": "Unable to start auto download. Download using this link: /var/www/html/w/images/DocBookExport/foobar.pdf" } }
"Success" is probably not the right word. Also, I would rather not let the whole world know the exact whereabouts of files on my server (although it is standard and probably not too dangerous to divulge).