Add Long-Term Validation (LTV) information for a signature in Xamarin

Long-term Validation (LTV) enables validating a signature on a document at the time it was signed at any time in the future, regardless of any changes made to technology specifications in the future. When LTV is added to a signature, the trusted root certificate that is used has its sign-time status captured and stored inside the PDF document. Regardless of the certificate's expiry or revocation status in the future, the LTV enabled signature guarantees the validity of the signature at the time it was signed.

To add Long-Term Validation (LTV) information for a signature (these examples assume and use an existing DocTimeStamp for LTV addition):

VerificationOptions opts = new VerificationOptions(VerificationOptions.SignatureVerificationSecurityLevel.e_compatibility_and_archiving);
opts.AddTrustedCertificate(in_trusted_cert_path);
/* By default, we only check online for revocation of certificates using the newer and lighter 
OCSP protocol as opposed to CRL, due to lower resource usage and greater reliability. However, 
it may be necessary to enable online CRL revocation checking in order to verify some timestamps
(i.e. those that do not have an OCSP responder URL for all non-trusted certificates). */
opts.EnableOnlineCRLRevocationChecking(true);
VerificationResult timestamp_verification_result = doctimestamp_signature_field.Verify(opts);
if (!doctimestamp_signature_field.EnableLTVOfflineVerification(timestamp_verification_result))
{
	Console.WriteLine("Could not enable LTV for DocTimeStamp.");
	return false;
}
doc.Save(in_outpath, SDFDoc.SaveOptions.e_incremental);

Digital signatures
Full code sample which demonstrates using the digital signature API to digitally sign, certify, and/or verify PDF documents.