test.cs

[HttpGet]
[Route("Prepare")]
public DocumentData Prepare()
{
  // create a new CustomerData object and serialize it to JSON
  var customer = new CustomerData {
    Name = "Smith",
    FirstName = "John",
    Street = "Main Street 1",
    City = "New York",
    Zip = "10001",
    Country = "United States"
  };

  var customerJson = JsonSerializer.Serialize(customer);

  byte[] documentBytes;

  using (var tx = new ServerTextControl()) {
    tx.Create();
    tx.Load("App_Data/template.tx", StreamType.InternalUnicodeFormat);

    // create a new MailMerge object and merge the JSON data
    var merge = new MailMerge {
      TextComponent = tx,
      FormFieldMergeType = FormFieldMergeType.Preselect,
      RemoveEmptyFields = false,
      RemoveEmptyImages = false
    };

    merge.MergeJsonData(customerJson);

    // save the document
    tx.Save(out documentBytes, BinaryStreamType.InternalUnicodeFormat);
  }

  var documentBase64 = Convert.ToBase64String(documentBytes);
  return new DocumentData { Name = "template.pdf", Document = documentBase64 };
}