I have received a document that has been edited by striking through text to be deleted and underlining text to be added. Is this something to do with track changes? I want to edit out and add in text but can't get rid of the current formatting?

The great big dog chased the blue crazy fox over the wall. I want to delete 'great' and add 'crazy'. On my document, the word 'great' shows as strikethrough but doesn't seem to show that in this message.

Any help will prevent me seeing my psychiatrist!