You should be able to ShellExecute the dwg file so it opens with its associated program which is Autocad.
Code:
Option Explicit
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 Const SW_HIDE As Long = 0
Private Const SW_SHOWNORMAL As Long = 1
Private Const SW_SHOWMAXIMIZED As Long = 3
Private Const SW_SHOWMINIMIZED As Long = 2
Private Sub Command1_Click()
ShellExecute Me.hwnd, "open", "C:\Users\Public\Test1.dwg", vbNullString, "C:\", SW_SHOWNORMAL
End Sub