如何在PDF中处理UnauthorizedAccessException？

Question

private void AssignEventHandlers()
{
   this.btnLocation.Click += new EventHandler(OnBrowse);
   this.btnExport.Click += new EventHandler(OnExport);
}
private void OnExport(object sender, EventArgs e)
{
    Document document = new Document();
    document.AddTitle("Test PDF Creator");
    using (FileStream stream = new FileStream(Path.Combine(this.txtFilePath.Text, "Example.pdf"), FileMode.Create, FileAccess.Write))
    {
        PdfWriter writer = PdfWriter.GetInstance(document, stream);
        document.Open();
        PdfPTable table = new PdfPTable(3);
        PdfPRow rowItem = null;
        PdfPCell[] cell = null;
        Phrase phrase = null;
        foreach (ListViewItem listItem in this.lvTest.Items)
        {
           cell = new PdfPCell[3];
           phrase = new Phrase(listItem.Text);
           cell[0] = new PdfPCell();
           cell[0].AddElement(phrase);
           phrase = new Phrase(listItem.SubItems[1].Text);
           cell[1] = new PdfPCell();
           cell[1].AddElement(phrase);
           phrase = new Phrase(listItem.SubItems[2].Text);
           cell[2] = new PdfPCell();
           cell[2].AddElement(phrase);
           rowItem = new PdfPRow(cell);
           table.Rows.Add(rowItem);
        }
        document.Add(table);
        document.Close();
    }
}