test.cs

[HttpGet]
public IActionResult MergeDocument()
{
    // create a ServerTextControl
    using (TXTextControl.ServerTextControl tx = new TXTextControl.ServerTextControl())
    {

        tx.Create();

        // load the template
        tx.Load("App_Data/template.tx", TXTextControl.StreamType.InternalUnicodeFormat);

        // create the mail merge engine
        using (TXTextControl.DocumentServer.MailMerge mm = new TXTextControl.DocumentServer.MailMerge())
        {
            // connect to ServerTextControl instance
            mm.TextComponent = tx;

            // merge data
            var jsonData = System.IO.File.ReadAllText("App_Data/data.json");
            mm.MergeJsonData(jsonData);
        }

        byte[] bDocument = null;

        // save in the internal format
        tx.Save(out bDocument, TXTextControl.BinaryStreamType.AdobePDF);

        // create memory stream from byte array
        MemoryStream stream = new MemoryStream(bDocument);

        stream.Position = 0;
        //Download Word document in the browser
        return File( stream, "application/pdf", "results.pdf");
    }
}