Stop To Open Dynamically Created PDF In Browser

i create a pdf dynamically it's perfect but the problem is that i want to open this pdf in popup but it cant't open in popup it open direct in browser. my code is below.

CLASS file
public class clsCreatePDF
{
public clsCreatePDF()
{
//
// TODO: Add constructor logic here
//
}
public string CreatePDF(string imagename)
{
HttpContext.Current.Response.ContentType = "application/pdf";
Document doc = new Document();
string fileName = Convert.ToString(DateTime.Now.Year + DateTime.Now.Month + DateTime.Now.Day + DateTime.Now.Hour + DateTime.Now.Minute + DateTime.Now.Second + DateTime.Now.Millisecond);
//string te = HttpContext.Current.Request.PhysicalApplicationPath + "PostCard\PostcardPDF\" + fileName + ".pdf";
PdfWriter.GetInstance(doc, new FileStream(HttpContext.Current.Request.PhysicalApplicationPath + "PostCard\PostcardPDF\" + fileName + ".pdf", FileMode.Create));
PdfWriter.GetInstance(doc, HttpContext.Current.Response.OutputStream);
doc.Open();
PdfPTable maintable = new PdfPTable(1);
maintable.DefaultCell.BorderColor = iTextSharp.text.BaseColor.BLACK;
// maintable.DefaultCell.Height = Convert.ToSingle(306)
//maintable.DefaultCell.PaddingTop = 10
///'''''''''''' inner table start '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
PdfPTable table = new PdfPTable(3);
maintable.AddCell(table);
table.DefaultCell.BorderColor = iTextSharp.text.BaseColor.WHITE;
// table.DefaultCell.Padding = 10
//PdfPCell imageCell1_1 = new PdfPCell(Image.GetInstance(HttpContext.Current.Server.MapPath("~/PostcardImage/smallimages/2257Bluehills.jpg")), true);
PdfPCell imageCell1_1 = new PdfPCell(Image.GetInstance(HttpContext.Current.Server.MapPath("~/PostcardImage/smallimages/" + imagename )), true);
imageCell1_1.Colspan = 2;
imageCell1_1.BorderColor = iTextSharp.text.BaseColor.WHITE;
imageCell1_1.VerticalAlignment.ToString("middle");
imageCell1_1.Border = 0;
imageCell1_1.PaddingLeft = 12;
imageCell1_1.PaddingTop = 12;
imageCell1_1.PaddingBottom = 0;
table.AddCell(imageCell1_1);
PdfPCell imagecell1_2 = new PdfPCell(Image.GetInstance(HttpContext.Current.Server.MapPath("~/PostcardImage/garmond1.jpg")), true);
imagecell1_2.BorderColor = iTextSharp.text.BaseColor.WHITE;
imagecell1_2.Border = 0;
table.AddCell(imagecell1_2);
// table.AddCell("1.2")
//PdfPCell imageCell2 = new PdfPCell(Image.GetInstance(HttpContext.Current.Server.MapPath("~/PostcardImage/bigimages/2257Bluehills.jpg")), true);
PdfPCell imageCell2 = new PdfPCell(Image.GetInstance(HttpContext.Current.Server.MapPath("~/PostcardImage/bigimages/"+ imagename )), true);
imageCell2.Colspan = 3;
imageCell2.BorderColor = iTextSharp.text.BaseColor.WHITE;
imageCell2.Border = 0;
imageCell2.PaddingTop = 12;
imageCell2.PaddingLeft = 30;
imageCell2.PaddingRight = 30;
table.AddCell(imageCell2);
//table.AddCell("1.3")
//table.AddCell("1.4")
//table.AddCell("2.1")
//table.AddCell("2.2")
// table.AddCell("")
PdfPCell imagecell3_1 = new PdfPCell(Image.GetInstance(HttpContext.Current.Server.MapPath("~/PostcardImage/garmond1.jpg")), true);
imagecell3_1.BorderColor = iTextSharp.text.BaseColor.WHITE;
imagecell3_1.Border = 0;
table.AddCell(imagecell3_1);
//table.AddCell("")
//PdfPCell imageCell3_2 = new PdfPCell(Image.GetInstance(HttpContext.Current.Server.MapPath("~/PostcardImage/smallimages/2257Bluehills.jpg")), true);
PdfPCell imageCell3_2 = new PdfPCell(Image.GetInstance(HttpContext.Current.Server.MapPath("~/PostcardImage/smallimages/" + imagename )), true);
imageCell3_2.Colspan = 2;
imageCell3_2.BorderColor = iTextSharp.text.BaseColor.WHITE;
imageCell3_2.Border = 0;
imageCell3_2.PaddingTop = 12;
imageCell3_2.PaddingRight = 12;
table.AddCell(imageCell3_2);
//table.AddCell("2.3")
//table.AddCell("2.4")
//table.AddCell("3.1")
//table.AddCell("3.2")
//table.AddCell("3.3")
//table.AddCell("3.4")
///'''''''''''''''''''''''''''''''' inner table clase''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
PdfPCell mainimgcell = new PdfPCell(table);
// mainimgcell.Colspan = 2
//maintable.AddCell("hi")
//mainimgcell.BorderColor = iTextSharp.text.BaseColor.RED
doc.Add(maintable);
//doc.Add(table)
doc.Close();
// HttpContext.Current.Response.Redirect("PostcardPDF/" + fileName + ".pdf");
return fileName;
}
}
CS page
if (imgupload.FileContent.Length > 0)
{
string fileName = "";
string pdfname = "";
//set Imagename by adding milliseconds too so that no overwrite in images directory.
fileName = DateTime.Now.Year + DateTime.Now.Month + DateTime.Now.Day + DateTime.Now.Hour + DateTime.Now.Minute + DateTime.Now.Second + DateTime.Now.Millisecond + Path.GetFileName(imgupload.PostedFile.FileName.ToString().Trim());
//Resize images and store it in different directories
ResizeImages objResizeImage = new ResizeImages();
objResizeImage.ResizeImage(fileName, imgupload.PostedFile.InputStream);
objResizeImage = null;
//*****************************Create PDF **************
clsCreatePDF objcreatepdf = new clsCreatePDF();
pdfname = objcreatepdf.CreatePDF(fileName);
Session["pdfname"] = pdfname;
objcreatepdf = null;
//*****************************end *********************
}

ASPX page is below

<tr>
<td>
</td>
<td>
<asp:Button ID="btnCancel" runat="server" Text="Cancel" PostBackUrl="~/usermodule/Dashboard.aspx" />
<asp:Button ID="btnCreate" runat="server" Text="Create and Preview New PostCard"
OnClick="btnCreate_Click" />
<asp:Button ID="btnshow" runat="server" Style="display: none" />
<cc1:ModalPopupExtender ID="popupProductDetails" runat="server" PopupControlID="pnlPostcard"
BackgroundCssClass="modalBackground" TargetControlID="btnshow" CancelControlID="btnCancelProductDetails" />
</td>
</tr>
<tr>
<td colspan="2">
<asp:Panel ID="pnlPostcard" CssClass="modalPopup" runat="server" Width="80%" Height="80%"
Style="display: none">
<table>
<tr>
<td>
<iframe id="Postcardframe" runat="server" scrolling="yes" width="750px;" height="100%">
</iframe>
</td>
</tr>
<tr>
<td style="text-align: right; width: 10%;">
<asp:Button ID="btnCancelProductDetails" Text="Cancel" runat="server" />
</td>
</tr>
</table>
</asp:Panel>
</td>
</tr>