How do I automatically print on both sides of the paper using Windows?
In your software's File menu, click Print, select the product, and click Properties or Preferences. Click the Finishing tab, select the 'Print on both sides' check box, and click OK to print. Note that if only manual duplex appears, the duplex unit may not be installed correctly or the media type may not be supported. (Pages 8-9)
From the official HP Laserjet Pro 400 Mfp M425 manual, page 8
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