Rename file when copied

Hi Experts!
Need your help I just copied and modify this code;
What I want is to add sumting on the file name, without changing, file path, original file name and file extension

Say;

I get the file

D: \Docs\Memo.docx

I can paste it to the fnpath with a changed filename

C: \_Temp\ Memo_BPMC-0001.docx

Heres the code
Any help will be highly appreciated
Thanks in advance

Private Sub CommandButton1_Click()
Dim fn
Dim FSO As Object
Dim DOC_NUM As String
Dim fnpath As String
fnpath = Application.Path
fnpath = tempPath & "C: \_Temp\"
fn = Application.GetOpenFilename
If fn = False Then
    MsgBox "Nothing Chosen"
Else
     TextBox1.Value = fn     
    Set FSO = CreateObject("scripting.filesystemobject")
    FSO.CopyFile Source:=fn, Destination:=fnpath
    TextBox3.Value = fnpath
End If    
End Sub