The replace text as you type of the Autocorrect option on the Proofing tab.
Many Microsoft office applications support Autocorrect. Autocorrect has a feature that allows you to add and delete words that do not follow abbreviation rules. For example, a frequently used word like Mark Smith from the University of Illinois can be replaced by a shorthand typed phrase like MSI. To assign or delete an abbreviation, you should click the File tab and then go options. Select proofing and click on the autocorrect options.
