test.cs

private Envelope ExtractEnvelopeFromPDF(byte[] document)
{
    using (TXTextControl.ServerTextControl tx = new TXTextControl.ServerTextControl())
    {
        tx.Create();

        var loadSettings = new TXTextControl.LoadSettings
        {
            EmbeddedFiles = new EmbeddedFile[] { },
        };

        tx.Load(document, TXTextControl.BinaryStreamType.AdobePDF, loadSettings);

        var embeddedFile = loadSettings.EmbeddedFiles
            .FirstOrDefault(ef => ef.FileName.StartsWith("tx-hash_"));

        if (embeddedFile != null)
        {
            return JsonConvert.DeserializeObject<Envelope>(Encoding.UTF8.GetString((byte[])embeddedFile.Data));
        }
    }

    return null;
}