How to get text Yunus Emre Şiirleri.pdf in C# ?

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Test_WebBrowser
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            this.webBrowser1.DocumentCompleted += webBrowser1_DocumentCompleted;
            this.textBox_URL.Text = @"http://google.com";
        }

        void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
        {
            HtmlAgilityPack.HtmlDocument d = new HtmlAgilityPack.HtmlDocument();
            d.LoadHtml(this.webBrowser1.DocumentText);
            foreach (var item in d.DocumentNode.DescendantsAndSelf())
            {
                this.textBox_Parse.Text += item.Name + " " + item.NodeType + Environment.NewLine;
            }
        }

        private void button_Go_Click(object sender, EventArgs e)
        {
            if (this.textBox_URL.Text.Length > 0)
            {
                this.webBrowser1.Navigate(this.textBox_URL.Text);
            }
        }
    }
}