In my time, I have seen many ugly forms and documents created in Word. One of the most egregious document bloopers I see is uneven or broken horizontal lines. Bad lines in a document are a sure sign of someone attempting to use Word like a typewriter.
Using Word like a typewriter is at best time-consuming and at worst frustrating. For example, suppose you want to create a line at the top of your document. Many books or reports put a line below the book title or chapter that appears at the top of the page. If you try to do this using the underline character on your keyboard, it won't work well at all.
But there is a better way. Actually, you can create lines that have nothing to do with the underline character in several ways:
1. Put a border on your text.
2. Create a table with a line on only one side.
3. Use the line tool on the Drawing toolbar.
For example, to create your line in your header, choose View|Header and Footer. Now type your book title and highlight it. Choose Format|Borders and Shading. In the Borders tab, select your line options from the drop down lists and click where you want the border in the Preview area. In the Apply to drop-down, be sure to click Paragraph, and click OK.
If you wanted to create a line under three words with one word left justified, one centered, and one right justified, your best bet would be to use a table. Choose Table|Insert|Table and create a one row table with three columns. Type each word into a cell and left, center, or right justify it in the cell. Now choose Format|Borders and Shading and add a bottom border.
Finally, if you need to create a diagonal line or some other line that can't be done another way, you can use the Line tool on the Drawing toolbar. Just be aware that because it's a free-floating line, it can take quite a bit of time to adjust it correctly with your mouse, so the line ends up where you want it.