PdfDigitalSignatureFieldName Property

Gets or sets the signature field name in the PDF document. By default, it is null and a predefined field name is used. When the document already contains an empty signature field with this name, for example a form prepared with a field for each signer, the signature is placed in that field, on its page and in its rectangle, with the text and image of Appearance. A field that is already signed or that is not a signature field is refused

public string FieldName { get; set; }