you add code Close event of the Document (on VBA->ThisDocument, past this code):
Private Sub Document_Close()
Dim strFile As String
'
' Change strFile to the Path and document name.
' the Extension should be (.docm, macro-enabled document)
'
' on this demo, i am saving it as "new.docm" on user's Document folder
'
strFile = Environ$("userprofile") & "\documents\new.docm"


' save it
Me.SaveAs2 saveToFileName(strFile), wdFormatXMLDocumentMacroEnabled
End Sub




Private Function saveToFileName(ByVal strFile As String) As String
    Dim file As String
    Dim ext As String
    Dim i As Integer, s As String
    ' get the extension
    i = InStrRev(strFile, ".")
    If i <> 0 Then
        ext = Mid$(strFile, i)
    End If
    ' get only the path+filename (without extension)
    file = Replace$(strFile, ext, "")
    ' new file has date on it
    s = file & Format$(Date, "_dd_mm_yyyy") & ext
    i = 1
    ' loop until we get "New" file
    Do While Len(Dir$(s)) <> 0
        s = file & Format$(Date, "_dd_mm_yyyy") & "(" & i & ")" & ext
        i = i + 1
    Loop
    saveToFileName = s
End Function