Private Declare Function ShellExecute Lib "shell32.dll" Alias "ShellExecuteA" _
    (ByVal hWnd As Long, ByVal lpOperation As String, ByVal lpFile As String, _
    ByVal lpParameters As String, ByVal lpDirectory As String, _
    ByVal nShowCmd As Long) As Long
 
  Private Function OpenWithLinkedApp(ByVal lOwnerHWND As Long, _
    ByVal sFile As String, Optional ByVal sVerb As String = "open") As Boolean
 
    OpenWithLinkedApp = ShellExecute(lOwnerHWND, sVerb, sFile, "", "", 1) > 32
  End Function
 
Private Sub Command1_Click()
OpenWithLinkedApp 0, "D:\Stadtwald\Revierbuch_gesamt.pdf"
End Sub