The HP OfficeJet Pro 9120e (Ink, Colour) does support duplex printing. This feature is known as automatic two-sided printing or duplex printing, and it is enabled through the printer settings.

To ensure duplex printing is available, you need to:
- Check the printer properties in the Control Panel or Devices and Printers section on your computer.
- Ensure that the «Duplex Unit» or «Automatic Two-Sided Printing» option is enabled under the Device Settings or Printer Preferences tab.

This feature allows the printer to automatically print on both sides of the paper, which is a standard capability of the HP OfficeJet Pro 9120e.