' The command button would look like this:
Private Sub Command1_Click()
    Close_External_Application "Microsoft Word"
End Sub

Declare Function FindWindow Lib "User" (ByVal lpClassName As Any, ByVal _
    lpWindowName As Any) As Integer
Declare Function GetWindowTask Lib "User" (ByVal hWnd As Integer) As Integer
Declare Function PostAppMessage Lib "User" (ByVal hTask As Integer, ByVal wMsg _
    As Integer, ByVal wParam As Integer, lParam As Any) As Integer
Public Const WM_QUIT = &H12


Function Close_External_Application(ByVal strCaptionTitle As String) As Boolean
Dim intWindowHandle As Integer
Dim intTaskHandle As Integer
Dim intPostReturnValue As Integer
' set defaults
Close_External_Application = False

' get handle of window matching caption
intWindowHandle = FindWindow(0&, strCaptionTitle)

If (intWindowHandle <> 0) Then
    ' window found
    intTaskHandle = GetWindowTask(intWindowHandle)
    intPostReturnValue = PostAppMessage(intTaskHandle, WM_QUIT, 0, 0&)
    ' set return value
    Close_External_Application = True
End If
End Function