SetPageBox 方法

Writes a new rectangle for the named page box (MediaBox / CropBox / BleedBox / TrimBox / ArtBox) on the current page.

Call UpdatePage after to commit the change; required to crop or pad printable PDFs.

Wraps the corresponding PDFium API and exposes it as a TPdf instance member so consumers do not have to manage FPDF_DOCUMENT handles directly.

• Always check Pdf1.Active before calling page-scoped operations; methods that require an open document raise EPdfError otherwise.
• Document-edit methods (AddPage / DeletePage / UpdatePage / CreateAnnotation) leave the in-memory document dirty — remember to call SaveToFile to persist.
• Class methods (LoadLibrary / UnloadLibrary / GetRecommendedV8Flags) can be called without a TPdf instance.