The main document contains both content that is identical in each copy and placeholders for the unique recipient information.
The main document is your starting point. The main document can be a letter, envelope, e-mail, or even a coupon. It contains:
Content that is identical in each copy, such as the main body text of a form letter. You only have to type this text once, regardless of how many letters you intend to print.
Placeholders for each recipient's information. For example, in a form letter, the address block and greeting name would be unique in each copy.