Few days ago, I realized that once the text is selected cannot be replaced with new ones  typed in MS Word, and probably in other MS Office products. This is very annoying options. Then I realized that the option for that is unchecked. I am pretty sure I didn’t uncheck the option, so the other reason would be after update installation.

However, I wanted to back previous feature since I need that option, specially when you try to replace some text in Word Equation. So in order to return the previous option to replace the highlighted text with new one, you should go to:

File->Options->Advanced