HP LaserJet Pro 400 color Printer M451 series - Manual (Page 79)

4. Place the paper in the tray and make sure
that it is flat at all four corners. Slide the side
paper width guides so that they align with the
paper-size marking in the bottom of the tray.
Slide the front paper length guide so that it
pushes the stack of paper against the back of
the tray.
5. Push down on the paper to make sure that
the paper stack is below the paper limit tabs
on the side of the tray.
6. Slide the tray into the product.
ENWW Load paper trays 61