I don't know what the function is called in English, but Word has a very useful function for correcting and editing. In French it's called "Suivi de modifications." You will find it in the Tools menu or click Ctrl + Cap + R.
When you do, a toolbar will open and the document will go into a mode where anything you insert, delete or change will appear as a correction and you can add commentaries. The best part about it is that, when you send it by e-mail to your colleague, he/she will be able to read the changes you have made, and choose to accept some or all of them without much work at all. A lifesaver.
That's the English name of this.