Thread:Extension talk:Pdf Export/Unable to generate PDF when using the Toolbar on side/reply

This seems to be related to the underscore‒space equivalence/conversion in Mediawiki. A workaround that does the job in my case is to add, between the following two lines in extensions/PdfExport/PdfExport_body.php, if ($dopdf) { $wgOut->setPrintable; (approx. line 111) the new line array_walk($pages, function(&$val, $key) {$val = strtr($val, '_', ' ');}); which converts underscores to spaces. This requires PHP ≥ 5.3 because of the anonymous function (a. k. a. closure) created by the  keyword, but it could easily be rewritten using.