How to Add a Line to a Header in Word

1. Double-click directly on the existing header at the top of the document, or if a header has not yet been created, double-click at the very top of the page just outside of the top margin. This will open a special header/footer view of the document and open the Header & Footer Tools Design tab on the Word ribbon at the top of the screen.
2. Select any existing text in the header by single-clicking outside of the left margin area using the white arrow pointer.
3. Click the 'Home' tab on the Word ribbon at the top of the screen and then click the 'Borders' button arrow in the paragraph group area of the ribbon. Select the 'Bottom Border' option to place a bottom border line directly underneath the header text.
4. Click the 'Borders' button again and choose 'Borders and Shading' at the bottom of the menu to select options that will change the thickness or the style of the line.Click in the style area to change the design of the line or click in the width box to change the thickness (or point size) of the line. Once you've made your selections, click on the line in the preview area to update the existing line. Click 'OK.'