index.aspx.cs

private void MergeTemplate(string templateName, string JsonData)
{
    // creating a new ServerTextControl and MailMerge class
    using (ServerTextControl tx = new ServerTextControl())
    {
        tx.Create();
        MailMerge mailMerge = new MailMerge();
        mailMerge.TextComponent = tx;

        // load the template
        mailMerge.LoadTemplate(Server.MapPath("templates/" + templateName),
            FileFormat.InternalUnicodeFormat);

        // create a new DataSet object
        DataSet ds = new DataSet();
        XmlDocument doc;

        // convert the JSON string to an XML document
        // object using Newtonsoft.Json
        try
        {
            doc = JsonConvert.DeserializeXmlNode(JsonData);
            lblError.Visible = false;
        }
        catch (Exception exc)
        {
            lblError.Visible = true;
            lblError.Text = exc.Message;
            DocumentViewer1.Visible = false;
            return;
        }

        // convert the XML to a DataSet
        XmlNodeReader reader = new XmlNodeReader(doc);
        ds.ReadXml(reader, XmlReadMode.Auto);

        // merge the template with the DataSet
        mailMerge.Merge(ds.Tables[0]);

        // load the resulting document into the DocumentViewer
        byte[] data;
        mailMerge.SaveDocumentToMemory(out data, BinaryStreamType.InternalUnicodeFormat, null);
        DocumentViewer1.LoadDocumentFromMemory(data, FileFormat.InternalUnicodeFormat);
    }
}