First, you'll need a reference to the word  object model. Then I use this
code to add a document  based on a particular template:

Private Sub CommandButton1_Click()
Set mobjWordApp = New Word.Application
With mobjWordApp
.Visible = True
.WindowState = wdWindowStateMaximize
.Documents.Add Template:="C:\Case prep\standardackv4.dot"
End With
End Sub

You'll need .Documents.Open to use an existing document, I think.