test.cs

TXTextControl.LoadSettings ls = new TXTextControl.LoadSettings() {
  ApplicationFieldFormat = TXTextControl.ApplicationFieldFormat.MSWord };

string jsonData = System.IO.File.ReadAllText("data.json");

using (TXTextControl.ServerTextControl serverTextControl =
       new TXTextControl.ServerTextControl()) {
  serverTextControl.Create();
  serverTextControl.Load("template.docx", TXTextControl.StreamType.WordprocessingML, ls);

  using (MailMerge mailMerge = new MailMerge()) {
    mailMerge.TextComponent = serverTextControl;
    mailMerge.MergeJsonData(jsonData);
  }

  // export document as PDF
  serverTextControl.Save("results.pdf", TXTextControl.StreamType.AdobePDF);
}