In microsoft word, when you highlight existing text you want to replace, you are in a. automatic mode. b. basic mode. c. typeover mode. d. insert mode.

The correct answer is C. Typeover mode

This is when you select a text and can then type over it and it automatically replaces it with what you're writing. It also creates a little box that lets you edit the selected part easily if that's what you need with things like bold or italic or change the text color.