Need help in downloading pdf through ajax call

See more:

C#

Ajax

itextsharp

ASP.NET4

Below is my aspx page

<%@ Page Title="" Language="C#" MasterPageFile="~/Site1.Master" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="CHEWGB.Default" %>
<asp:Content ID="Content1" ContentPlaceHolderID="head" runat="server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">
    <style type="text/css">
        body {
            background-color: none;
        }

        .control-label {
            color: black;
            font-weight: 600;
            font-size: 17px;
            text-align: center;
            font: bolder;
        }

        .submitBtn {
            padding: 10px 20px 11px !important;
            font-size: 21px !important;
            background-color: orange;
            font-weight: bold;
            text-shadow: 1px 1px #F36C8C;
            color: black;
            border-radius: 100px;
            -moz-border-radius: 100px;
            -webkit-border-radius: 100px;
            border: 1px solid #F36C8C;
            cursor: pointer;
            box-shadow: 0 1px 0 rgba(255, 255, 255, 0.5) inset;
            -moz-box-shadow: 0 1px 0 rgba(255, 255, 255, 0.5) inset;
            -webkit-box-shadow: 0 1px 0 rgba(255, 255, 255, 0.5) inset;
        }

            .submitBtn:hover {
                -webkit-transform: scale(1.3);
                transform: scale(1.3);
            }

            #dvProgressBar {
              position: fixed;
              z-index: 1031;
              top: 50%;
              left: 50%;
              transform: translate(-50%, -50%);
            }
            #pageloadicon {
              position: fixed;
              z-index: 1031;
              top: 50%;
              left: 50%;
              transform: translate(-50%, -50%);
            }
            #pageloadicon:after{
                  content: "Please wait..";
                  display: block;
                  position: absolute;
                  top: 50%;
                  left: 50%;
                  transform: translate(-50%, -50%)
                }

            #myOverlay{position:absolute;top:0;left:0;height:100%;width:100%;}
            #myOverlay{background:black;backdrop-filter:blur(3px);opacity:.3;z-index:2;display:none;}
    </style>

    <table style="background-color: none; border-collapse: separate; border-spacing: 20px; font: bold; font-size:larger">
        <tr>
            <td align="center">
                <asp:Label ID="Label1" runat="server" CssClass="control-label" Text="Enter Number : " BackColor="Aquamarine"></asp:Label>
            </td>
            <td align="center">
                <asp:TextBox ID="txtPoNumber" runat="server" autocomplete="off"></asp:TextBox>
            </td>
            <td align="center">
                <asp:Button ID="submtBtn" CssClass="submitBtn"  runat="server" Text="Submit" Style="float: right;" />
            </td>
        </tr>
    </table>

    <div id="myOverlay"></div>
    <div id="dvProgressBar"></div>
    <div id="pageloadicon"><img src="pageLoad.gif"/></div>

  <br style="clear:both" />

      <link href = "Css/jquery-ui.css" rel = "stylesheet"/>
      <script src = "Scripts/jquery-1.10.2.js"></script>
      <script src = "Scripts/jquery-ui.js"></script>
      <script type="text/javascript">

          $(document).ready(function () {
              $('#pageloadicon').hide(); 
              

              $("input[id$='submtBtn']").click(function () {
                   $('#myOverlay').show();
                 $('#dvProgressBar').html('<img src="myloading.gif"/><br/>Please wait while we collect the data and generate pdf..');
                  $.ajax({
                      type: "POST",
                      url: "Default.aspx/startPdfGenerate",
                      data: {},
                      async: true,
                      contentType: "application/json; charset=utf-8",
                      dataType: "json",
                      success: function (response) {
                           alert(response);
                      },
                      complete: function () {
                           $('#myOverlay').hide();
                          $("#dvProgressBar").css("display", "none");
                      },
                      error: function (response) {
                          $('#myOverlay').hide();
                          $("#dvProgressBar").css("display", "none");
                          alert("Something went wrong");
                          alert(response.status);
                      }
                  });
              });
          });
    </script>
</asp:Content>

Below is my code behind

using iTextSharp.text;
using iTextSharp.text.pdf;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Web;
using System.Web.Services;

namespace CHEWGB
{
    public partial class Default : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {

        }


        [WebMethod]
        public static string startPdfGenerate()
        {
            try
            {
                string status = string.Empty;
                status = GetQualityScannedImg();

                return status;
            }
            catch (Exception ex)
            {
                return "failure";
            }
        }
        public static string GetQualityScannedImg()
        {
            try
            {
                //Initialize the PDF document object.
                using (Document pdfDoc = new Document(PageSize.A4, 10f, 10f, 45f, 25f))
                {
                    PdfWriter writer = PdfWriter.GetInstance(pdfDoc, System.Web.HttpContext.Current.Response.OutputStream);
                    writer.PageEvent = new ITextEvents();

                    PdfDestination pdfDest = new PdfDestination(PdfDestination.XYZ, 0, pdfDoc.PageSize.Height, 1f);
                    pdfDoc.Open();

                    PdfAction action = PdfAction.GotoLocalPage(1, pdfDest, writer);
                    writer.SetOpenAction(action);

                    DirectoryInfo dirInfo = new DirectoryInfo(@"\\Sharedfolder\Images");

                    //Excludes Hidden Files
                    FileInfo[] files = dirInfo.GetFiles().Where(file => (file.Attributes & FileAttributes.Hidden) == 0).ToArray();

                    Image img = null;

                    float documentWidth = pdfDoc.PageSize.Width - pdfDoc.LeftMargin - pdfDoc.RightMargin;
                    float documentHeight = pdfDoc.PageSize.Height - pdfDoc.TopMargin - pdfDoc.BottomMargin;

                    foreach (FileInfo filePath in files)
                    {

                        //Add the Image file to the PDF document object.
                        img = Image.GetInstance(filePath.FullName);
                        img.ScaleToFit(documentWidth, documentHeight);
                        pdfDoc.Add(img);
                        break;
                    }
                    pdfDoc.Close();

                    img = null;
                    //Download the PDF file.
                    HttpContext.Current.Response.ContentType = "application/pdf";
                    HttpContext.Current.Response.AddHeader("content-disposition", "attachment;filename=ImageExport.pdf");
                    HttpContext.Current.Response.Cache.SetCacheability(HttpCacheability.NoCache);
                    HttpContext.Current.Response.Write(pdfDoc);
                    //HttpContext.Current.Response.End();
                    HttpContext.Current.ApplicationInstance.CompleteRequest();
                }
                return "success";
            }
            catch (Exception ex)
            {
                return "failure";
            }
        }  
    }
}

The issue here is pdf file is not generating after ajax call.

What I have tried:

Instead of ajax i tried with normal onclick function of the button to check the code function. It works fine and pdf is getting generated. But when i use ajax it is not downloading.