2. Enter the header content in header editing mode, and then select it. Click Start to find the place as shown in the figure below, and click the bottom border. At this point, you will see a template line below the text. Double-click the left key in other blanks to exit the header editing mode.
3. As shown in the figure below, the horizontal line was successfully added. If necessary, you can also choose an upper horizontal line or other types of lines.