private void addTsa(PdfSignatureAppearance signAppearance)
{
var es = new PrivateKeySignature(_asymmetricKeyParameter, "SHA-256");
var tsc = new TSAClientBouncyCastle(SignatureData.TsaClient.Url, SignatureData.TsaClient.UserName, SignatureData.TsaClient.Password);
MakeSignature.SignDetached(signAppearance, es, _chain, null, null, tsc, 0, CryptoStandard.CMS);
}