How do I download pdf from pdfdrive.net automatically ?

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var request = (HttpWebRequest)WebRequest.Create("https://www.pdfdrive.net/irodov-problems-in-general-physics-d24882553.html");
					request.Method = "GET";
					request.AllowAutoRedirect = false;
					request.UserAgent = "Mozilla/5.0 (Windows NT 6.1; rv:7.0.1) Gecko/20100101 Firefox/7.0.1";
					request.Headers.Add("DNT", "1");
					request.Accept = "text/html,application/xhtml+xml,application/xml";
	
					using(var response = (HttpWebResponse)request.GetResponse())
					using(var stream = response.GetResponseStream())
					using (var sr = new StreamReader(stream, Encoding.UTF8))
					{
					    responseStr = sr.ReadToEnd();
					    response.Close();
					    if (stream != null)
					        stream.Close();
					    sr.Close();
					    
					    File.WriteAllText(Environment.CurrentDirectory + "/pip.txt", e.Url.ToString() + responseStr);
					}