Duplexing does not work from the ADF; Cannot make two-sided copies; Scanner duplex is broken
How to make duplexed copies; The printer has a built-in duplexer. However, the scanner's Automatic Document Feeder (ADF) is simplex. It only scans the front side of the page.
To make duplex copies, either from a double-sided original to a double-sided copy OR from single-sided originals to a double-sided copy, you have to use the scanner flatbed and manually flip the original.