Originally Posted by Charles Kenyon

Glad you found a solution. For future reference, you can apply a top or bottom border as a part of a paragraph style. This acts as a horizontal rule. It will stretch from left indent to right indent (usually the page or column margins). By clicking on "More" in the Replace dialog, you can go to Format > Style to use the Replace function to replace or apply styles in a document. Styles are very much worth learning if you are using Word much at all.

Understanding Styles in Microsoft Word