How do I change the length of a border in Microsoft word?

To change the length of a border in Microsoft Word, first select the paragraph or text box you want to modify. Then, go to the "Design" tab (or "Home" tab) and click on "Borders" in the Paragraph group. Choose "Borders and Shading," where you can adjust the border's length by changing the settings for the specific border you want to alter, such as adding space or modifying the paragraph alignment. You can also use the ruler to drag the ends of the border if it's a custom line drawn.