After you create your form letter, you can use it as the basis for a mail merge by selecting New > Mail Merge or add it to an existing mail merge by clicking the View drop-down, selecting Mail Merges, and editing a mail merge.
To edit a mail merge template, do the following:
In the Merge Template Name box, type the name of the new mail merge template.
In the Merge Template Description box, you can also include a brief description of the template.
Click in the body of the document to edit the mail merge template.
Click Page Setup to launch the Microsoft Word Page Setup dialog.
Click Save to save your changes.
Click Close.