There are times in which it is beneficial to set limits on the editing that can be done to the format of document, especially when the file is being used by many people and format needs to be set a certain way for the final product.
1. In the Word file you wish to restrict editing, click on the "Review" tab and click "Restrict Editing."
2. You will see "Restricting Formatting and Editing" pane at the right sidebar providing numerous options to restrict editing.
3. Under "Formatting restrictions" enable "Limit formatting to a selection of styles" option. For configuring advance options click "Settings."
4. Click "Formatting Restrictions" dialog will appear, here you can restrict formatting to the desired styles and prevent others from modifying styles and change formatting of the document. Scroll through the list and disable the desired options. You can also use the recommended settings by clicking "Recommended Minimum."
5. Under "Formatting" you can enable several options that let you to Allow AutoFormat usage which overrides formatting restrictions, Block Theme or Scheme switching, and Block Quick Style Set Switching. Click "OK" to continue.
6. From "Editing restrictions" enable "Allow only this type of editing in the document" option and from its list choose desired option.
These instructions, along with illustrations and instructions for additional features of Conditional Formatting for Message Lists, can also be found in SharePoint > Software Users Group > Shared Documents > Word > Restricting Editing.