The paper size options offered by Word are determined by your printer
driver. If your printer doesn't offer a specific envelope size as a built-in
paper size, then you'll have to create it as a custom size. Some printers
allow you to define new paper sizes in the driver.
This may also vary with the version of Word: in Word 2003, the Paper tab of
Page Setup offers only a very few envelope sizes (those provided by my
printer driver), but the size list in the Envelope Options dialog of Tools |
Letters and Mailings | Envelopes and Labels offers many more, including 6
3/4.
