Canon LBP7210Cdn Manual page 236

IMPORTANT
Do not load the paper stack which exceeds the load limit mark lines.
Be sure that the paper stack does not exceed the load limit mark lines. If the paper stack exceeds
the load limit mark lines, this may result in misfeeds.
Insert the paper drawer into the printer.
Push it into the printer firmly.
CAUTION
Precautions when inserting the paper drawer
Be careful not to catch your fingers.
Step 2: Registering the Size of Paper
This printer's paper drawer cannot automatically detect the paper size. Therefore, you need to register the size of
the loaded paper.
Register the paper size using the following procedure.