Canon S400 Reference Manual page 190

Check 1
Is the paper too thick?
Thick paper does not feed. You cannot attempt to print on paper or other
media thicker than 105g/m
Check 2
Is the sheet feeder overloaded?
The number of sheets you can load in the auto sheet feeder depends on
the media you are using. The media does not feed correctly if you exceed
the prescribed number of sheets.
Check 3
Did you raise the paper rest?
Before you load media other than envelopes in the auto sheet feeder, you
should always raise the paper rest. If you do not raise the paper rest before
loading, the media does not completely enter the paper feed slot during
feeding.
2
.
Number of sheets that can be loaded
Paper does not feed from auto sheet feeder
Troubleshooting - Paper Jams or Does Not Feed 190