test.cs

public class TextControlProcessing {
  public static void Merge(ProcessingRequest request) {

    using (TXTextControl.ServerTextControl tx = new TXTextControl.ServerTextControl()) {
      tx.Create();

      // simulate long process
      Thread.Sleep(3000);

      // create document or use MailMerge to generate larger document
      tx.Text = "My created document.";

      byte[] data;
      tx.Save(out data, TXTextControl.BinaryStreamType.AdobePDF);

      request.StoreDocument(data);
    }

    request.Processed = true;
    request.Update();

    Task.Run(() => FireAndForgetWebHook(request));
  }

  private static void FireAndForgetWebHook(ProcessingRequest request) {
    HttpClient client = new HttpClient();

    var json = JsonConvert.SerializeObject(request);
    var data = new StringContent(json, Encoding.UTF8, "application/json");

    client.PostAsync(request.WebHookUrl, data);
  }
}