Even if you place originals in the ADF or on the exposure glass correctly, margins of a few millimeters on all four sides of the original might not be copied.
Missing Image Area

Leading edge: 3.0±2.0 mm (0.12±0.08 inches)
Trailing edge: 3.0±2.0 mm (0.12±0.08 inches) (4.2±2.0 mm (0.17-0.08 inches) in Duplex mode)
Left edge: 2.0±1.5 mm (0.08±0.06 inches)
Right edge: 2.0+2.5/-1.5 mm (0.08+0.10/-0.06 inches)