HP LaserJet 4345 Multifunction Printer series - Manual (Page 147)

3. Insert the optional envelope feeder firmly into the MFP until it latches into position. Pull
gently on the optional envelope feeder to be sure that it is securely in place.
Removing the optional envelope feeder
Use these steps to remove the optional envelope feeder from the MFP.
To remove the optional envelope feeder
1. Press the release button that is located on the left side and pull the optional envelope
feeder away from the MFP.
2. Replace the plastic envelope-entrance cover in the printer and close tray 1.
Loading envelopes in the optional envelope feeder
Use these steps to load envelopes in the optional envelope feeder.
ENWW Envelope feeder 133