Когда окно notepad?а не имеет фокуса ввода, то тогда твой код терпит неудачу. Нижеприведенный код в случае неудачи не вставляет в notepad символ ?V?:
Public Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Public Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
Public Sub Exemple()
Dim y As Long, hwnd As Long
y = Shell("notepad.exe", vbNormalFocus)
hwnd = FindWindow("Notepad", vbNullString)
AppActivate y
If hwnd <> 0 Then
SendMessage hwnd, 273, 770, 0 'WM_COMMAND = 273, Ctrl+V = 770
End If
End Sub