Options for one signature: the field it goes into, the signature properties it records, the sub-filter and the digest algorithm.
public sealed class PdfSignatureOptions
ISO 32000-2 §12.8.1, Table 255, §12.8.3 and §12.7.5.5. The defaults sign a new invisible signature field named Signature1
(or the first such name the form does not use) with adbe.pkcs7.detached and the digest the signer's key calls for
(SHA-256 for RSA and P-256), and record the time of signing.
kind:method, kind:property, kind:ctor. Press Esc to clear.AppearanceGets or sets the visible appearance of the signature; null (the default) makes a new field invisible (an empty rectangle on the first page) and leaves an existing field's appearance as it is.CertificationGets or sets the changes the document permits after this signature, which makes it a certification signature; null (the default) makes an approval signature. A certification signature shall be the document's first signature.ContactInfoGets or sets how to contact the signer (ContactInfo), or null.DigestAlgorithmGets or sets the digest algorithm for the byte range digest and the signed attributes: SHA-256, SHA-384, SHA-512 or, as HashAlgorithmNames named SHA3-256, SHA3-384 and SHA3-512, the SHA-3 digests. null (the default) picks the one the signer's key calls for: SHA-384 for an ECDSA key on P-384, SHA-512 on P-521, SHA-256 otherwise.FieldLockGets or sets the fields this signature locks, written as the signature field's lock dictionary; null (the default) writes none. A field that already has a lock dictionary is locked by it whatever this says, and cannot take another.FieldNameGets or sets the fully qualified name of the signature field to sign. An unsigned signature field of that name is signed; when the form has no field of that name, a new invisible signature field is created under it. null (the default) creates a new field named SignatureN, N the lowest number from 1 the form does not use.LocationGets or sets the host name or physical location of the signing (Location), or null.ReasonGets or sets the reason for signing (Reason), or null to leave it out.SignerNameGets or sets the name of the signer (Name), or null to leave it out: Table 255 says to use it "only when it is not possible to extract the name from the signature", which carries the certificate.SigningTimeGets or sets the time of signing written as the signature dictionary's M entry; null (the default) writes the current time. The time is not verifiable: a timestamp is.SubFilterGets or sets the encoding of the signature (SubFilter): AdobePkcs7Detached (the default) or a PAdES signature, EtsiCadesDetached, which raises the document to PDF 2.0.TimestampClientGets 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.