Click on the Track Changes icon in the Reviewing toolbar to turn on the Track Changes feature.

Select the word and delete it

Two things will happen in Web, Print Layout and Reading Views:

* A bar will appear at the beginning of the sentence indicating an edit in that line of text.

* The deletion will be in a balloon located in the right margin.

Or if you are in the Normal or Outline Views:

* A line will appear at the beginning of the sentence indicating an edit in that line of text.

* The word will change color and have a line through it.