WordPad doesn’t have an inbuilt option for “horizontal line.”
However, you can insert the horizontal line into your WordPad by following these steps:
Open the WordPad document.
Place the cursor where you need a horizontal line.
Press and hold the Hyphen key on your keyboard until it fills the current line.
Remember that this one will add a dashed line. If you want a straight line, then you need to press and hold both the Hyphen and Shift keys until it fills the current line.