Restricting Formatting and Editing
If you want to protect parts of a document, yet grant permission for specific users to change other parts of the document, you can set restriction and protection options in the Restrict Formatting and Editing pane. If you only want to prevent users from formatting a document, you can also restrict users from making any formatting changes or limit formatting to a selection of styles.
Restrict Formatting Changes
Open the document you want to protect.
Click the Review tab.
Click the Restrict Editing button.