Canon PRO-10 Series Manual page 87

(4) Slide the paper guides
PAPER in the center of the manual feed tray WITH THE PRINT SIDE
FACING YOU.
(5) Slide the paper guides
Do not slide the paper guides too hard against the paper. The paper may not be fed properly.
Important
Always load paper in the portrait orientation (C). Loading paper in the landscape orientation
(D) can cause paper jams.
(B) to open them, and load ONLY ONE SHEET OF
(B) to align them with both sides of the paper.