Typically, you edit a document using Insert mode. This means text to the right of the insertion point moves to the right as you type new text. Insert mode adds text, but it does not erase anything.
Press the Insert key (located to the right of the Backspace key) once; you can change your computer to Overtype mode.
When your computer is in Overtype mode, text you type replaces any existing text to the right of the insertion point and erases it.
You can tell which mode you are in by looking at the Status bar at the bottom of the screen.
Insert mode is the default mode for editing in Word. It is useful for adding and changing words. It is also the most flexible because it does not erase existing text. Insert mode is recommended for most editing.
Overtype mode is useful when replacing a word or series of words. It is particularly useful when you want to change the ending of a sentence.
Be careful. You can easily type over text you want to keep.
If you find yourself in Overtype mode and start to panic, press the Insert key.