test.cs

private bool SaveSignedPDF(TXTextControl.Web.MVC.DocumentViewer.Models.SignatureData data, Envelope envelope)
{
    try
    {
        using (TXTextControl.ServerTextControl tx = new TXTextControl.ServerTextControl())
        {
            tx.Create();
            tx.Load(Convert.FromBase64String(data.SignedDocument.Document), TXTextControl.BinaryStreamType.InternalUnicodeFormat);

            var embeddedFile = new EmbeddedFile($"tx-hash_{data.UniqueId}.txt", Encoding.UTF8.GetBytes(JsonConvert.SerializeObject(envelope)), null)
            {
                Relationship = "Data",
                MIMEType = "application/json"
            };

            X509Certificate2 cert = new X509Certificate2("App_Data/textcontrolself.pfx", "123");

            var saveSettings = new TXTextControl.SaveSettings
            {
                EmbeddedFiles = new EmbeddedFile[] { embeddedFile },
                CreatorApplication = "TX Text Control Sample Application",
                SignatureFields = new DigitalSignature[]
                {
                    new TXTextControl.DigitalSignature(cert, null, "txsign")
                }
            };

            var savePath = Path.Combine("App_Data/signed", $"{data.UniqueId}.pdf");
            Directory.CreateDirectory(Path.GetDirectoryName(savePath));
            tx.Save(savePath, TXTextControl.StreamType.AdobePDF, saveSettings);
        }
        return true;
    }
    catch (Exception)
    {
        return false;
    }
}