Olá amigo, faça o seguinte.

Declare a constante a function:

 

Public Const SW_SHOW As Long = 5
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

Depois, no evento chame a ShellExecute.

 

Private Sub Button_Click()
  dim i&
  i& = ShellExecute(0,"open",[arquivo ex: c:meuarq.doc],"","",SW_SHOW)
End Sub

 

Espero ter ajudado.

Att.