test.cs

string jsonData = System.IO.File.ReadAllText("data.json");
textControl1.Load("template.tx", TXTextControl.StreamType.InternalUnicodeFormat);

using (MailMerge mailMerge = new MailMerge()) {
  mailMerge.TextComponent = textControl1;
  mailMerge.MergeJsonData(jsonData);
}

foreach(TXTextControl.Table table in textControl1.Tables) {
  table.RemoveEmptyColumns();
}