Download File from https web site

var httpRequest = (HttpWebRequest)WebRequest.Create(@"https://yoursite/fileToDownload.ext");
         httpRequest.Credentials = new NetworkCredential("username", "password", "domainname");
         var httpResponse = (HttpWebResponse)httpRequest.GetResponse();

         var downloadStrm = httpResponse.GetResponseStream();
         var donloadStrm = new StreamReader(downloadStrm);
         // Do whatever you want with donloadStrm
         downloadStrm.Close();