Canon BJ-10sx - Manual (Page 30)

Printing On Envelopes, Transparencies, or Thick
Paper
You must load envelopes, transparencies, and thick paper from the
bottom slot of the printer.
To load envelopes, transparencies, or thick paper, follow these steps.
(The illustrations show how to load an envelope; the steps are exactly
the same for transparencies or thick paper.)
1. Make sure the printer is turned off and the top cover is closed.
2. Grasp the front of the printer with one hand and position the
printer stand with your other hand.
3. Turn the printer stand so it is perpendicular to the back of the
printer and set the printer on it's back.