tx.cs

// create a business object that is used
// as the data source
Invoice invoice = new Invoice() { Name = "Report" };

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

    LoadSettings ls = new LoadSettings() {
        ApplicationFieldFormat = ApplicationFieldFormat.MSWord
    };

    // load the created template
    tx.Load("template.docx", StreamType.WordprocessingML, ls);

    // create a new MailMerge engine
    using (MailMerge mailMerge = new MailMerge())
    {
        // connect to ServerTextControl
        mailMerge.TextComponent = tx;

        // merge the template that is loaded with
        // the business object
        mailMerge.MergeObject(invoice);                
    }

    // export the document as PDF
    tx.Save("test.pdf", StreamType.AdobePDF);
}