HP LaserJet Enterprise 600 Printer M603 series - Manual (Page 133)

4. Select the Print on both sides (manually)
check box. Click the OK button to print the
first side of the job.
5. Retrieve the printed stack from the output bin,
and place it with the printed-side facing up in
Tray 1.
6. On the control panel, press the OK button to
print the second side of the job.
Automatically print on both sides with Windows
NOTE: This information applies only to products that have an automatic duplexer.
1. On the File menu in the software program,
click Print.
ENWW Basic print tasks with Windows 117