HP Deskjet F4580 All-in-One Printer - Manual (Page 32)

Remove all paper from the paper tray.
b. Load envelopes.
Insert one or more envelopes into far-right side of the paper tray, with
envelope flaps on left and facing up.
Slide stack of envelopes forward until it stops.
Slide paper-width guide to the right against stack of envelopes until it stops.
2. View the animation for this topic.
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Paper basics