test.cs

[HttpPost]
public ActionResult GenerateForm(int Id)
{
    Customer customer;
    byte[] baCreatedFormDocument;

    // get customer by Id from database
    using (var db = new LiteDatabase(Server.MapPath("~/App_Data/customers.db")))
    {
        var col = db.GetCollection<Customer>("customers");

        col.EnsureIndex(x => x.Id);
        customer = col.Query()
            .Where(x => x.Id == Id)
            .SingleOrDefault();
    }

    using (TXTextControl.ServerTextControl tx = new TXTextControl.ServerTextControl())
    {
        tx.Create();

        // the form template
        tx.Load(Server.MapPath("~/App_data/form_template.tx"), 
                TXTextControl.StreamType.InternalUnicodeFormat);

        // loop through all form fields of each text part
        foreach (IFormattedText textPart in tx.TextParts)
        {
            foreach (FormField formField in textPart.FormFields)
            {
                // get associated value of property; check for null!
                var propertyValue = 
                    typeof(Customer).GetProperty(formField.Name)?.GetValue(customer);

                // cast values for specific form field types
                switch (formField.GetType().ToString())
                {
                    case "TXTextControl.TextFormField": // accepts strings
                    case "TXTextControl.SelectionFormField":
                        if (propertyValue != null)
                            ((TextFormField)formField).Text = (string)propertyValue;
                        break;

                    case "TXTextControl.CheckFormField": // accepts bool
                        if (propertyValue != null)
                            ((CheckFormField)formField).Checked = (bool)propertyValue;
                        break;

                    case "TXTextControl.DateFormField": // accepts Win32 file dates
                        if (propertyValue != null)
                        {
                            if (Convert.ToDateTime(propertyValue.ToString())
                                != DateTime.MinValue)
                                ((DateFormField)formField).Date =
                                    Convert.ToDateTime(propertyValue.ToString());
                        }
                        break;
                }
            }
        }

        // export form
        tx.Save(out baCreatedFormDocument, BinaryStreamType.AdobePDF);
    }

    // return the PDF as an attachment
    MemoryStream pdfStream = new MemoryStream();
    pdfStream.Write(baCreatedFormDocument, 0, baCreatedFormDocument.Length);
    pdfStream.Position = 0;

    Response.AppendHeader("content-disposition", 
                          "attachment; filename=form_" + Id + ".pdf");
    
    return new FileStreamResult(pdfStream, "application/pdf");
}