Canon PIXMA MX394 Online Manual page 38

(4) Slide the right paper guide
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 (B). Loading paper in the landscape orientation
paper jams.
Note
Do not overload paper by stacking until the top of the stack touches the paper guides.
Load small size paper, such as 4" x 6" (10 x 15 cm), by pushing it in all the way to the back of the front tray.
(A) to align the paper guides with both sides of the paper stack.
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(C) can cause