HP Deskjet 6540 Color Inkjet Printer - Manual (Page 104)

11.6 Automatic two-sided printing
To print a two-sided document automatically, one of the following accessories must
be attached to the printer:
Automatic Two-Sided Printing Accessory
Auto Two-Sided Print Accessory with Small Paper Tray
The two-sided printing accessories only support certain paper types. For a list of
supported paper types, see the documentation that came with the accessory.
If a two-sided printing accessory is not attached to the printer or you are printing on
an unsupported paper type, use manual two-sided printing .
Printing
Follow these instructions to print a two-sided document:
1. Open the Print dialog box, and then select the Layout panel.
HP Deskjet 6500 series printers User's Guide
104