A signature field: the place of a digital signature, signed when its value is a signature dictionary.
public sealed class PdfSignatureField : PdfTerminalField
ISO 32000-2 §12.7.5.5, Tables 235 to 237; field type Sig (PDF 1.3). A signature field "shall never refer to more than one
annotation"; one with several widgets keeps them all and records SignatureFieldMultipleWidgets. Signature dictionaries,
seed values and validation are read raw here.
kind:method, kind:property, kind:ctor. Press Esc to clear.IsSignedGets a value indicating whether the field has a signature value.IsVisibleGets a value indicating whether the signature is visible: it has a widget whose rectangle has a width or height and whose Hidden and NoView flags are clear.LockGets the fields locked when the field is signed (Lock, PDF 1.5), or null.SeedValueGets the seed value dictionary that constrains the signature applied to the field (SV, PDF 1.5), as stored, or null.SignatureDictionaryGets the signature dictionary the field holds when it is signed (V, inheritable), or null.