HP Color LaserJet Enterprise CM4540 MFP series - Manual (Page 110)

Load paper trays
Load Tray 1
CAUTION: To avoid jams, never add or remove paper from Tray 1 during printing.
1. Open Tray 1.
2. Fold out the tray extension to support the
paper and set the side guides to the correct
width.
90 Chapter 6 Paper and print media ENWW