How to add and remove horizontal lines between sections of the document

Enter three or more special characters on a new line and then press Enter, Word automatically expands these characters to a line. A style of this line depends on the characters:

• Three or more "*" - dotted line
• Three or more "=" - double line
• Three or more "~" - wavy line
• Three or more "#" - thick decorative line
• Three or more "-" or "_" - thick single line

These lines often used in Word documents, but you can simply remove them if you understand: this is not a line - this is a paragraph border (for more details see How to use paragraph borders and shading).

And you can turn on/off AutoReplace of these symbols to lines. Do one of the following:

• Then Word makes an AutoReplace, it shows the AutoCorrect Options button. You can click in it and choose Stop Automatically Creating Border Lines:
  
• Do the following:

   1.   On the File tab, click the Options button:

   2.   In the Word Options dialog box, on the Proofing tab, under AutoCorrect options, click the AutoCorrect Options... button:

   3.   In the AutoCorrect dialog box, on the AutoFormat As You Type tab, in the Apply as you type group, check or uncheck Border lines to turn on or off this option:

See also this tip in French: Comment ajouter et supprimer des lignes horizontales entre des sections du document.