You must proceed as follows:
Choose "File"/"Page Setup". In the dialog coming up then choose your printer in the first drop-down and a page size with "Auto Duplex" in the second drop-down". Then click OK and choose "File"/"Print" again. Now you can choose duplex.
You must proceed as follows:
Choose "File"/"Page Setup". In the dialog coming up then choose your printer in the first drop-down and a page size with "Auto Duplex" in the second drop-down". Then click OK and choose "File"/"Print" again. Now you can choose duplex.