Flash is included
To opt into flash, append
prefs=http://prefs.webconverger.com/2015/click-to-play.js to your configuration.
Flash from 17.x lives in /usr/lib/mozilla/plugins/
sudo mv libflashplayer.so $WEBC_CHECKOUT/usr/lib/mozilla/plugins/libflashplayer.so
Check download was over TLS, e.g. https://fpdownload.adobe.com
PDF support is included
However please think twice about using PDF on the Web! HTML is the best format to store your documents.