PLDA respects the PDF specification where the page boxes are defined as follows:
Nevertheless, PLDA simplifies the approach to boxes and uses only those valuable in real printer’s life. Everything behind the Trim Box is considered as bleed unless the Bleeds dialog is used to set up the bleeds. For successful imposition of a bleeded document the Trim Box must be specified. All important applications can provide the Trim Box correctly. If the Trim Box is not specified, you can use Crop Box that can be set by Adobe Acrobat tools.