To select from within the list of available header styles, click the ‹Insert› Menu button in the right upper corner of the window. Select an existing heading style from this menu. To rename the style, click ‹Naming› and choose a name. For naming convenience, the default naming will be applied. On the ‹Format› tab of the header style list, in the ‹Style name› field, under the heading style name, enter ‹Letterhead› as the Style Name. The Style Name and a description must not exceed 10 characters. When you are finished with any of the available header styles, close Microsoft Word. At the top of the header style list, click the ‹Format› button and select the ‹Insert› menu option, or go to the format› page in your document. Click on the ‹Add Style› icon to add a new style. How to Add Letterhead to a Word Document In Microsoft Office, go to the Ribbon. In the ribbon, click File > Properties. In the left pane of the application, click Document Properties.