For Residential and Commercial document styles ONLY. The Modern style is created with the idea of it being emailed more often than sent via postal mail.
In an ideal world, it would be nice if an address in the header of an invoice, proposal, PO, or statement would fit it a window envelop when the page is folded in exact thirds. With certain letterhead and margin settings greater than 1.5 inches this becomes impossible because the address will be too far down on the page because of the space necessary to skip the letterhead. Letterhead and margin settings are found on the Company, Advanced Options Window, Print Tab.
When using the default settings and using your own pre-printed letterhead, a good rule of thumb is to make your first fold about the height of the envelop itself. Based on these settings the first fold may need to be adjusted, some trial and error will be necessary.