The main document contains the text and other items you want to be identical in each version of the merged document. The data source contains the information that varies in each version, such as the names and addresses of each recipient of a form letter. You insert special instructions, called merge fields, into the main document to instruct MS-Word where to print the variable information from the data source. When you merge the data source and the main document, MS-Word replaces merge fields in the main document with the appropriate information from the data source. Once you have set up the envelopes or mailing labels the way you want, Word automates the merging process, collecting information from the data source and setting up the printing placement where you indicated in the main document.
Word then prints the envelopes or labels.
While creating form letters is the most common reason to merge documents, you can also use the Mail Merge feature to prepare other kinds of merged documents, such as catalogs, parts lists, directory lists, forms, or invoices. Once you're familiar with the basic process, you can explore these other possibilities for mail merge. In the first step, you set up the main document, which contains the text, punctuation, and other items that remain the same in each version of the form letter. Open the document you want to use as the main document. You can open an existing letter, or you can begin a new letter based on a template you select.