1. First, open the edited word document and click the start arrow in the lower right corner of the style ribbon.

2. A style window will pop up. Click the style management icon in the pop-up window.

3. In the pop-up window, click the "Restrictions" tab, as shown in the following figure.

4. In the style label setting interface, click "Select All", then check "Format only allowed styles", and then click "Restrict".

5. After setting, click OK to pop up a window, asking for a protection password, and click OK.

6. You can find that all the buttons on the ribbon are gray, indicating that the document format can no longer be edited.