HP Officejet 350 All-in-One Printer - Manual (Page 146)

2. In the File Name box, type a name for the file.
N
For letterhead, use extension .LHD.
N
For second sheets, use extension .SND.
3. Click the OK button.
Note:`Additionally, you can save the image to a file type supported
by a drawing application (e.g., PCX for Microsoft Paintbrush) as well
as edit the image in the drawing application, and then use Eclipse
FAX SE to convert the file to .LHD or .SND format (open the file in
Eclipse FAX SE, then save it as file type LHD or SND).