Master pages provide the underlying format and background for pages. All new form designs are created with a default master page, which is applied to the first page. Additional pages are formatted according to the layout of the default master page unless you create a different master page to use.
A form design can contain any number of master pages, each having a unique layout. If some of the pages need different layouts or boilerplate objects, you can create a master page for each unique layout.

Assigning additional master pages to complex form designs