THPDFHeadlessDocument.AddSignatureField

function AddSignatureField(const Name: UnicodeString; PageIndex: Integer;
  const Rectangle: THPDFRectangle): Integer;

Creates a real terminal signature field and page widget, returning its zero-based form-field index

Name must be a unique nonempty terminal name without dots; PageIndex selects an existing indirect page and Rectangle supplies finite nonzero PDF coordinates

Existing AcroForm and annotation arrays retain their fields and widgets; documents without an AcroForm receive a new indirect AcroForm dictionary

Object, field, name, serialization, and aggregate output budgets are prepared before graph changes; cancellation and rejected creation preserve the original graph

Encrypted sources require annotation modification permission or owner authentication; new widgets cannot be added to a certified document

Use SetSignatureFieldAppearance for a visible caption and SignToFile or SignPFXToFile for atomic signature publication