test.cs

TXTextControl.DocumentServer.MailMerge mm = new TXTextControl.DocumentServer.MailMerge();
mm.TextComponent = textControl1;

textControl1.Load("invoice.tx", TXTextControl.StreamType.InternalUnicodeFormat);

Invoice invoice = CreateSampleInvoice();

// merge data into template
mm.MergeJsonData(JsonConvert.SerializeObject(invoice));

// create the XML
string xmlZugferd = invoice.CreateXml();

// get the required meta data
string metaData = MetaData.GetMetaData();

TXTextControl.SaveSettings saveSettings = new TXTextControl.SaveSettings();

// create a new embedded file
var zugferdInvoice = new TXTextControl.EmbeddedFile(
  "ZUGFeRD-invoice.xml",
  Encoding.UTF8.GetBytes(xmlZugferd),
  metaData);

zugferdInvoice.Description = "ZUGFeRD-invoice";
zugferdInvoice.Relationship = "Alternative";
zugferdInvoice.MIMEType = "application/xml";
zugferdInvoice.LastModificationDate = DateTime.Now;

// set the embedded files
saveSettings.EmbeddedFiles = new TXTextControl.EmbeddedFile[] {
  new TXTextControl.EmbeddedFile(
     "ZUGFeRD-invoice.xml",
     Encoding.UTF8.GetBytes(xmlZugferd),
     metaData) };

// export the PDF
textControl1.Save("test.pdf", TXTextControl.StreamType.AdobePDFA, saveSettings);