test.cs

// new non-UI ServerTextControl
using (TXTextControl.ServerTextControl tx = new TXTextControl.ServerTextControl()) {

    tx.Create();

    // loda a template
    tx.Load("App_Data/template.tx", TXTextControl.StreamType.InternalUnicodeFormat);

    // load data from file
    var sData = System.IO.File.ReadAllText("App_Data/data.json");

    // merge data
    using (TXTextControl.DocumentServer.MailMerge mm = 
           new TXTextControl.DocumentServer.MailMerge()) {
        mm.TextComponent = tx;
        mm.MergeJsonData(sData);
    }

    // save the document into a byte array
    byte[] document;
    tx.Save(out document, TXTextControl.BinaryStreamType.AdobePDF);
}