P Lamberti wrote:
I used to be able to highlight a section of text in a word document
then just start typing new text and it would automatically be put in
the place of the highlighted text (the highlighted text would be
replaced.) Now when I start typing after highlighting the text, the
highlighted text reamins and what I'am typing just gets inserted at
the front of the highlighted section.

In Tools Options Edit, check the box for "Typing replaces selection".

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Regards,
Jay Freedman
Microsoft Word MVP FAQ: http://word.mvps.org