Selection.PreviousSubdocument (Word)

Moves the selection to the previous subdocument.

If there isn't another subdocument, an error occurs.

If ActiveDocument.Subdocuments.Count >= 1 Then 
 ActiveDocument.ActiveWindow.View.Type = wdMasterView 
 Selection.EndKey Unit:=wdStory, Extend:=wdMove 
 Selection.PreviousSubdocument 
End If