Envelopes pose a problem when you're using a word processor. Their dimensions are different from your document's. So, you must use different page formatting for the envelope.
Fortunately, you don't need to calculate margins and then make complicated changes in Word. You just need to use Word's Envelopes feature. It will make all the adjustments for you. And all it takes is a few minutes!
To open the Envelopes Wizard, view the Mailings ribbon. Click Envelopes in the Create section.