Canon PRO-300 Series Online Manual page 128

5. Slide the paper guides (G) to open them, and load ONLY ONE SHEET OF PAPER in the
center of the manual feed tray WITH THE PRINT SIDE FACING YOU.
6. Slide the paper guides (G) to align them with both sides of the paper stack.
Do not slide the paper guides too hard against the paper. The paper may not be fed properly.
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