Sets DigestAlgorithm.
public PdfSignatureOptions WithDigestAlgorithm(HashAlgorithmName? digestAlgorithm)
SHA-256, SHA-384, SHA-512, SHA3-256, SHA3-384 or SHA3-512; null for the key's.
null
ISO 32000-2 §12.8.3.1, Table 260; ISO/TS 32001 §5.1.4.