HP Officejet 300 All-in-One Printer - Manual (Page 67)

Printing Envelopes
With Windows Applications
When using the HP OfficeJet to print envelopes from a Windows
application, be sure to choose envelopes as the media size (in the
Printer Options dialog box).
The HP OfficeJet automatically selects the correct Orientation when
you choose an envelope media size. The Orientation controls in the
HP OfficeJet Printer Setup dialog box are grayed out when you
choose an envelope size.
You may, however, need to select printing orientation in your
software program. Some programs use a print setup dialog provided
by Windows to select common printer settings. This dialog does not
automatically default to the correct orientation for envelopes. If the
Orientation settings are not disabled (grayed out) when you select
envelopes, you must select the correct orientation in the software
program print setup dialog box.
Select Landscape orientation for the HP OfficeJet printer.