Gridview header text not taking hindi font when export to pdf

Hi,
I am tying to export gridview into pdf. But problem is that my
my row display hind text but header text is bot attacepting
hindi properly.

<asp:UpdatePanel ID="upmain" runat="server">
<Triggers>
<asp:PostBackTrigger ControlID="btnExportPDF" />
</Triggers>
<ContentTemplate>
<asp:GridView ID="GridView1" runat="server" Width="300" HeaderStyle-BackColor="#3AC0F2"
HeaderStyle-ForeColor="White" RowStyle-BackColor="#A1DCF2" AlternatingRowStyle-BackColor="White"
RowStyle-ForeColor="#3A3A3A" AutoGenerateColumns="false" Font-Names="Arial" Font-Size="12">
<Columns>
<asp:BoundField ItemStyle-Width="200px" DataField="Name" HeaderText="?????? ????." />
<asp:BoundField ItemStyle-Width="200px" DataField="HindiName" HeaderText="Hindi Name" />
</Columns>
</asp:GridView>
</ContentTemplate>
</asp:UpdatePanel>
<br />
<asp:Button ID="btnExportPDF" runat="server" Text="ExportToPDF" OnClick="btnExportPDF_Click" />

protected void Page_Load(object sender, EventArgs e)
{
DataTable dt = new DataTable();
dt.Columns.AddRange(new DataColumn[2] { new DataColumn("Name"), new DataColumn("HindiName") });
dt.Rows.Add("India", "????");
dt.Rows.Add("China", "???");
dt.Rows.Add("England", "???????");
dt.Rows.Add("Canada", "?????");
dt.Rows.Add("Russia", "???");
dt.Rows.Add("Japan", "?????");
GridView1.DataSource = dt;
GridView1.DataBind();
}

protected void btnExportPDF_Click(object sender, EventArgs e)
{
GridView1.AllowPaging = false;
GridView1.DataBind();

BaseFont bf = BaseFont.CreateFont(Environment.GetEnvironmentVariable("windir") + @"\fonts\MANGAL.TTF", BaseFont.IDENTITY_H, true);

iTextSharp.text.pdf.PdfPTable table = new iTextSharp.text.pdf.PdfPTable(GridView1.Columns.Count);
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);

//Set Font and Font Color
iTextSharp.text.Font font = new iTextSharp.text.Font(bf, 10, iTextSharp.text.Font.NORMAL);
font.Color = new iTextSharp.text.BaseColor(GridView1.HeaderStyle.ForeColor);
iTextSharp.text.pdf.PdfPCell cell = new iTextSharp.text.pdf.PdfPCell(new Phrase(12, cellText, font));

//Set Header Row BackGround Color
cell.BackgroundColor = new iTextSharp.text.BaseColor(GridView1.HeaderStyle.BackColor);

table.AddCell(cell);
}
table.SetWidths(widths);

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);

//Set Font and Font Color
iTextSharp.text.Font font = new iTextSharp.text.Font(bf, 10, iTextSharp.text.Font.NORMAL);
font.Color = new iTextSharp.text.BaseColor(GridView1.RowStyle.ForeColor);
iTextSharp.text.pdf.PdfPCell cell = new iTextSharp.text.pdf.PdfPCell(new Phrase(12, cellText, font));

//Set Color of row
if (i % 2 == 0)
{
//Set Row BackGround Color
cell.BackgroundColor = new iTextSharp.text.BaseColor(GridView1.RowStyle.BackColor);
}

table.AddCell(cell);
}
}
}

//Create the PDF Document
Document pdfDoc = new Document(PageSize.A4, 10f, 10f, 10f, 0f);
PdfWriter.GetInstance(pdfDoc, Response.OutputStream);
pdfDoc.Open();
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 override void VerifyRenderingInServerForm(Control control)
{
/* Verifies that the control is rendered */
}