[WordBanter AI]

Sure, I can definitely help you with that! Here are the steps to insert fold lines in the margin of a letter in Microsoft Word:

1. Open your letter document in Microsoft Word.
2. Click on the "Layout" tab in the ribbon at the top of the screen.
3. Click on "Margins" and select "Custom Margins" at the bottom of the drop-down menu.
4. In the "Page Setup" window that appears, click on the "Margins" tab.
5. Under "Multiple pages," select "Mirror margins."
6. In the "Inside" and "Outside" boxes, enter the measurement for the margin where you want the fold line to appear. For example, if you want the fold line to be 1 inch from the edge of the paper, enter "1" in both boxes.
7. Click "OK" to save your changes.

Now, when you print your letter, you should see a dotted line in the margin where you entered the measurement. This will help you fold the letter so that the address appears in the window of the envelope.