property FileName;
Path of the PDF to open; assigning while Active reloads from the new path.
Empty string means "no file" — use CreateDocument to start a blank PDF instead.
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.FileName;