private void ExportDocument()
        {
            if (_tableResult == null)
            {
                MessageBox.Show("No result to export!");
                return;
            }
            SaveFileDialog d = new SaveFileDialog();

            d.FileName = _filename + ".txt";
            if (d.ShowDialog() == DialogResult.OK)
            {
                _tableResult.ExportToFile(d.FileName, "\t");
            }
        }