VBA Excel - Run macro for copying formula in each file of a folder

Private Sub CommandButton1_Click()
Dim Filename, Pathname As String
Dim wb As Workbook

    Pathname = ActiveWorkbook.Path & "\Files\"
    Filename = Dir(Pathname & "*.xlsm")
    Do While Filename <> ""
        Set wb = Workbooks.Open(Pathname & Filename)
        DoWork wb
        wb.Close SaveChanges:=True
        Filename = Dir()
    Loop
End Sub

    Sub DoWork(wb As Workbook)
    With wb
    Dim rng
rng = "P4:P23"
.Sheets(1).Range("P4").Select

Selection.AutoFill Destination:=.Sheets(1).Range(rng)
    .Sheets(1).Range(rng).Select
       
    End With
End Sub