Master
documents in Word are documents that merge together and hold links to several smaller documents. Their purpose is to support the management of large documents by allowing the user to “fold” up the subdocuments into links, thereby leaving the master document with an organized framework.
To see how this works, first create a document that has several sections in it, denoted by typing some sort of heading on a line by itself. The
example we’re going to use here has some opening text, and then five sections denoted as
Section One through
Section Five. Before formatting, it looks like this:

This document will serve as our master document, while the sections inside of it will become our sub-documents