Gets or sets the client of the time-stamp authority that time-stamps the signature, or null (the default) for
none. With a client, once the signer returns the signature value, the authority is asked for a token over it, and the token is
added to the signature as its signature time-stamp unsigned attribute: with EtsiCadesDetached
that is a PAdES baseline B-T signature. The room for the token is reserved with
TokenSizeEstimate; the timestamp needs PDF 1.6.
public PdfTimestampClient? TimestampClient { get; set; }
ISO 32000-2 §12.8.3.3.1 (timestamp information as an unsigned attribute, PDF 1.6) and §12.8.3.4.3 b) (the signature timestamp "should be applied on the digital signature immediately after the signature is created"); RFC 3161 Appendix A, as updated by RFC 5816; ETSI EN 319 142-1 (B-T).