Do one of the following:
If you do not see the subdocument icon , click Master Document View on the Outlining toolbar.
Notes
Split a subdocument into two subdocuments
Notes
When you save the master document, Microsoft Word assigns a file name to the new subdocument based on the first characters in the subdocument's heading.
If you combine subdocuments and then split them back into separate documents, Word saves the split subdocument with a new file name.