Start>Control Panel>Printers and Faxes
rightclick your Panasonic printer and click Properties.
Click the Device Settings tab
Next to Auto - should be "letter" with a small down (v) arrow
Click it and you'll have dozens of custome format paper to select from.
Click Apply and OK.
Note: If your custom format paper size is not listed, then it cannot be done
for in this listing are the only drivers for that type of printer. You
could query
Panasonic if they have additional drivers for it at their website.