Macro Programming MS oficce 2010 Save AS

Hello I have a code that was created by one of the members here, and I am trying to figure out how to add to it.  What this code does is as soon as its opened, it generates a number and puts it to a log file, and this number is used as a invoice number on the cell N2.  But what I also need is also, that as soon as its opened, the file will be saved as an xslx documents so that the user can make any changes to the document and come back to it without the number being touched.  The main template will be stored somewhere and a user can open it up, and I want it to save as to an xslx to another location and close the xlsm file.  THe filename of the new file is going to be "invoice_strNum.

Can anyone help

Private Sub Workbook_Open()
    Const ForReading = 1
    Const ForAppending = 8
    Dim objFSO As Object
    Dim objFil As Object
    Dim strFilePath As String
    Dim strLast As String
    Dim strNum As String
    Dim strContents As String
    Dim arrLines
    strFilePath = ThisWorkbook.Path & "\log.txt"
    Set objFSO = CreateObject("Scripting.FileSystemObject")
    On Error Resume Next
    Set objFil = objFSO.getfile(strFilePath)
    On Error GoTo 0
    If objFil Is Nothing Then
        Set objFil = objFSO.createTextFile(strFilePath, ForWriting)
        objFil.writeline "1," & Environ("username") & "," & Now()
    Else
        Set objFil = objFSO.OpenTextFile(strFilePath, ForReading)
        strContents = objFil.ReadAll
        objFil.Close
        Set objFil = objFSO.OpenTextFile(strFilePath, ForAppending)
        arrLines = Split(strContents, vbCrLf)
        strLast = arrLines(UBound(arrLines) - 1)
        strNum = Val(Left(strLast, InStr(strLast, ",") - 1)) + 1
        objFil.writeline strNum & "," & Environ("username") & "," & Now()
    End If
    objFil.Close
    Sheets("EXPENSE FORM").Range("N2").Value = strNum
End Sub

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