ปัญหา iTextSharp: Export PDF จาก GridView ไม่สามารถแสดง ภาษาไทยได้

  protected void btnExportPDF_Click(object sender, EventArgs e)
    {
        GridView1.AllowPaging = Convert.ToBoolean(rbPaging.SelectedItem.Value);
        GridView1.DataBind();

         //Create a table
        iTextSharp.text.Table table = new iTextSharp.text.Table(GridView1.Columns.Count);
        table.Cellpadding = 5; 

        //Set the column widths 
        int[] widths = new int[GridView1.Columns.Count];
        for (int x = 0; x < GridView1.Columns.Count; x++)
        {
            widths[x] = (int)GridView1.Columns[x].ItemStyle.Width.Value ;
            string cellText = Server.HtmlDecode(GridView1.HeaderRow.Cells[x].Text);
            iTextSharp.text.Cell cell = new iTextSharp.text.Cell(cellText);
            //iTextSharp.text.Cell cell = new iTextSharp.text.Cell(new Phrase("Basic Account Information", FontFactory.GetFont(FontFactory.HELVETICA, 9, iTextSharp.text.Font.BOLD)));
            cell.BackgroundColor = new Color (System.Drawing.ColorTranslator.FromHtml("#008000"));
            table.AddCell(cell); 
        }
        table.SetWidths(widths);

                
        //Transfer rows from GridView to table
        for (int i = 0; i < GridView1.Rows.Count; i++)
        {
            if (GridView1.Rows[i].RowType == DataControlRowType.DataRow)
            {
                for (int j = 0; j < GridView1.Columns.Count; j++)
                {
                    string cellText = Server.HtmlDecode(GridView1.Rows[i].Cells[j].Text);
                    iTextSharp.text.Cell cell = new iTextSharp.text.Cell(cellText);

                    //Set Color of Alternating row
                    if (i % 2 != 0)
                    {
                        cell.BackgroundColor = new Color(System.Drawing.ColorTranslator.FromHtml("#C2D69B"));
                    }
                    table.AddCell(cell);
                }
            }
        }
		
        BaseFont EnCodefont = BaseFont.CreateFont(Server.MapPath("/font/ANGSA.TTF"), BaseFont.IDENTITY_H, BaseFont.EMBEDDED);
        Font Nfont = new Font(EnCodefont, 18, Font.NORMAL);
        Document pdfDoc = new Document(PageSize.A4, 10f, 10f, 10f, 0f);
        PdfWriter.GetInstance(pdfDoc, Response.OutputStream);
        pdfDoc.Open();
        pdfDoc.Add(new Paragraph("รายงานข้อมูลประจำวันที่ " + System.DateTime.Now.ToString("dd/MM/yyyy"), Nfont));
        pdfDoc.Add(table);
        pdfDoc.Close();  
        Response.ContentType = "application/pdf";
        Response.AddHeader("content-disposition", "attachment;filename=GridViewExport.pdf");
        Response.Cache.SetCacheability(HttpCacheability.NoCache);
        Response.Write(pdfDoc);
        Response.End();
    }

public class MyFontFactoryImpl : FontFactoryImp
    {
        Font defaultFont;
        public MyFontFactoryImpl()
        {

            BaseFont tahoma = BaseFont.CreateFont(@"C:\WINDOWS\Fonts\tahoma.ttf", BaseFont.IDENTITY_H, BaseFont.NOT_EMBEDDED);
            defaultFont = new Font(tahoma, 12);
           
        }
        public override Font GetFont(string fontname, string encoding, Boolean embedded, float size, int style, BaseColor color, Boolean cached )
        {
            return defaultFont;
        }
    }

    public class HtmlToPdf
    {
        string _html;
        public HtmlToPdf(string html)
        {
            if (!(FontFactory.FontImp is MyFontFactoryImpl))
                FontFactory.FontImp = new MyFontFactoryImpl();
            _html = html;
        }

        public void Render(Stream stream)
        {
            StringReader sr = new StringReader(_html);
            Document pdfDoc = new Document();
            PdfWriter.GetInstance(pdfDoc, stream);
            HTMLWorker htmlparser = new HTMLWorker(pdfDoc);
            pdfDoc.Open();
            htmlparser.Parse(sr);
            pdfDoc.Close();
        }

        public void Render(HttpResponse response, string fileName)
        {
            response.Clear();
            response.AddHeader("Content-Disposition", string.Format("attachment; filename={0}", fileName));
            response.ContentType = "application/octet-stream";

            Render(response.OutputStream);

            response.End();
        }
    }

protected void ImageButton2_Click(object sender, ImageClickEventArgs e)
    {
        StringWriter sw = new StringWriter();
        HtmlTextWriter hw = new HtmlTextWriter(sw);
        myGridView.AllowPaging = false;
        myGridView.DataBind();
        myGridView.RenderControl(hw);
        
        HtmlToPdf htmlToPdf = new HtmlToPdf(sw.ToString());

        htmlToPdf.Render(Response, "test.pdf");
    }

iTextSharp.text.Document document = null;
try
{
document = new iTextSharp.text.Document();
PdfWriter writer = PdfWriter.GetInstance(document, new FileStream("HelloWorld.pdf", FileMode.Create));
document.Open();
BaseFont baseFont = BaseFont.CreateFont(@"C:\WINDOWS\Fonts\angsau.TTF", BaseFont.IDENTITY_H, BaseFont.NOT_EMBEDDED, true);
Phrase phrase = new Phrase("ผู้กัน", new iTextSharp.text.Font(baseFont));
Paragraph paragraph = new Paragraph();
paragraph.Add(phrase);
document.Add(paragraph);
}
catch (Exception ex) {
throw ex;
}
finally
{
document.Close();
}