Signs the document and writes the signed file to stream, signing and writing asynchronously.
public Task SignAsync(Stream stream, IPdfSigner signer, PdfSignatureOptions? options = null, CancellationToken cancellationToken = default(CancellationToken))
Where to write, from its current position. It is not disposed.
Signs the digest, through SignDigestAsync(ReadOnlyMemory<Byte>, HashAlgorithmName, CancellationToken).
The field, the signature properties and the digest algorithm; null for the defaults.
Cancels the signing and the writes.
ISO 32000-2 §12.8.1, §12.8.3.3 and §12.8.3.4. Writes what Sign(Stream, IPdfSigner, PdfSignatureOptions?) writes; only the signer call and the writes to
stream are asynchronous. A cancelled or failed signer leaves the document as it was.