Word's default letter document template contains numerous unconventional format settings and automatic formats. A best advised strategy is to reset them all to conventional Standard Typescript Format definitions.
Begin with a blank document. To set default font (typeface and size), on the Home tab click the down and right arrow in the lower left-hand corner of the Font selections on its ribbon. Set font to preferred typeface, e.g., Courier New, font style to regular, size to 12 pts., font color to automatic, underline style none, uncheck any effects boxes. Then click the advanced tab and and reset if necessary: Character Spacing to 100% scale, Spacing normal, and Position normal. Uncheck kerning for fonts and no OpenType features, or none and default, respectively. When all settings are suitable, click the Set as Default button and select Set as default for all documents based on the Normal.dotm template.
Likewise, for the Paragraph dialogue on the home tab and its ribbon down right arrow. Indent and spacing tab, General, Alignment, Left, Outline Level, Body Text; Indentation, Left, 0", Right, 0", Special, None; and Spacing (line), Before, 0", After, 0", Line Spacing, Double, uncheck Don't add space between paragraphs; select tabs, set to default tab .5", click Line and Page Break tab, uncheck all boxes, especially the widow/orphan control check box, which is the root of all lines moving to another page. Then click Set as Default button and select as default for all documents based on the Normal.dotm template. These actions reset the default document template.
Also, consider setting page layout margins top and left to .75" so that the header and footer line spaces print outside the page body margins, results in exactly 25 content lines per page. Reset header to .5" from top and 0" from bottom of the the header box. Include page number insert in header, and . . . Slander, heck and calumny, the gdmf Word auto header/footer format.
Also, consider turning off AutoCorrect for replace two hyphens with dash, three periods with ellipsis points glyph, straight quote marks and apostrophes with SmartQuote marks, etc. Under the File menu, choose Options, select Proofing, select AutoCorrect options, select AutoFormat, and adjust whichever suits the intent. Like turn off replace straight quotes with SmartQuotes, replace fractions, points, ordinals, etc.
A lot to do, though once and done; and Word's template designers' true nefarious intent is to force upon users the learning of how to adjust documents and set layout options.
Corel Office WordPerfect is far less problematic and my preferred word processor program. Less verbose formatting, too, the Reveal Code feature is most much convenient for eliminating spurious codes that turn a document into a multi megabyte file the more it's edited and revised. Argh on Word.