Gets or sets the text shown, one line per line; null (the default) shows Digitally signed by and the
signer's name (SignerName, else the certificate's subject name), Date: and the signing
time, and Reason: and Location: when the options give them. An empty string shows no text.
public string? Text { get; set; }
ISO 32000-2 §12.8.1, Table 255 (Name, M, Reason, Location).