To print PDF forms double-sided:
When creating a PDF Export Profile from Exports -> Export Profiles or editing an existing one:
1. Check the box next to the "Duplex" option.
2. Click "Save".
Now, when printing, select the PDF Export Profile you just changed and the PDF export will be Duplex.
NOTE: If you have locked the Export Profile previously you will be unable to make any changes.
Your printer must have the capability to print double-sided in order for this feature to work.