Samsung SCX-5639FR-XAA - Manual (Page 63)

Media and tray
63 2. Menu overview and basic setup
2 Load the original face up into the document feeder. Make sure
that the bottom of the original stack matches the paper size
marked on the document input tray. 3 Adjust the document feeder width guides to the paper size.
Dust on the document feeder glass may cause black lines on
the printout. Always keep the glass clean (see "Cleaning the
machine" on page 103).