Private Sub openButton_Click(ByVal sender As Object, ByVal e As EventArgs) _
  Handles openButton.Click
        Try
            process_xl_file()
            GC.Collect()
            GC.WaitForPendingFinalizers()
            GC.Collect()
            GC.WaitForPendingFinalizers()
        Catch ex As Exception
            ShowInfoMessage(ex.Message)
        End Try
End Sub
 
Sub process_xl_file()
        Dim i, j As Integer
        Dim xl, wb, ws As Object
        Dim sourceFilePath As String = Path.Combine(sourceListBox.Tag.ToString, _
        sourceListBox.SelectedItem.ToString)
 
        wb = GetObject(sourceFilePath)
            xl = wb.Application
            xl.Visible = True
            wb.NewWindow()
            ws = wb.Sheets(1)
            For i = 1 To 3
                For j = 1 To 3
                    Console.WriteLine("Zelle in Zeile {0} / Spalte {1} ={2}", _
                        i, j, ws.Cells(i, j).Value)
                Next
            Next
            ws.Cells(4, 1).Value = Now
 
        wb.Windows(wb.Windows.Count).Close()
            wb.Save()
        wb.Close()
        If xl.Workbooks.Count = 0 Then xl.Quit()
 
End Sub