property FormFill;
Interface that lets your application supply forms-related callbacks (Beep, Invalidate, OutputDocFile, etc.).
Assign a custom implementation to override the default no-op handlers.
Wraps the corresponding PDFium API and exposes it as a TPdf instance member so consumers do not have to manage FPDF_DOCUMENT handles directly.
Pdf1.Active before calling page-scoped operations; methods that require an open document raise EPdfError otherwise.SaveToFile to persist.
if Pdf1.Active then
Pdf1.FormFill;