hook.cs

[HttpPost]
public bool WebHook([FromBody] object request) {

  dynamic ProcessingRequest = JObject.Parse(request.ToString());

  HttpClient client = new HttpClient();
  HttpResponseMessage responseMessage = 
    client.GetAsync(ProcessingRequest.RetrieveDocumentUrl.Value).Result;

  if (responseMessage.IsSuccessStatusCode) { 
    string data = responseMessage.Content.ReadAsStringAsync().Result;
    System.IO.File.WriteAllBytes(
      "App_Data/" + ProcessingRequest.Id.Value + ".pdf", Convert.FromBase64String(data));
    return true;
  }
  else
    return true;
}