Creates an unsigned signature field with one widget on page.
public PdfSignatureField AddSignatureField(string name, PdfPage page, PdfRectangle rectangle, PdfFieldOptions? options = null)
The field's fully qualified name, as for AddTextField(String, PdfPage, PdfRectangle, PdfFieldOptions?).
The page the widget is on, a page of this form's document.
The widget's rectangle, in default user space; an empty one makes the signature invisible.
The widget colours; null for the defaults.
ISO 32000-2 §12.7.5.5 (PDF 1.3) and §12.7.3, Table 225. A signature field (FT Sig, no V) merged with its
widget, whose appearance draws the widget's background and border; the form's SigFlags gets SignaturesExist. Otherwise
as AddTextField(String, PdfPage, PdfRectangle, PdfFieldOptions?) describes.