This example adds a subdocument named "Subdoc.doc" to the active document.
ActiveDocument.ActiveWindow.View.Type = wdMasterView
ActiveDocument.Subdocuments.AddFromFile _
Name:="C:\MyFolder\Subdoc.doc"
This example adds a password-protected subdocument named "MySubdoc.doc" to the active document on a read-only basis.
Selection.Range.Subdocuments.AddFromFile Name:="MySubdoc.doc", _
ReadOnly:=True, PasswordDocument:="MyPassword"