What the five PDF page boxes mean
MediaBox is the physical page canvas and is required, directly or through the page tree. CropBox defines the region normally displayed or printed and defaults to MediaBox. BleedBox describes the region needed when output extends beyond the trim. TrimBox is the intended finished page after cutting. ArtBox identifies meaningful artwork content rather than a manufacturing boundary.
When BleedBox, TrimBox, or ArtBox is absent, PDF readers treat it as CropBox. The inspector shows that default explicitly; it does not claim that the file contains a deliberately authored bleed or trim boundary.
How inherited boxes are reported
PDF page trees can store MediaBox, CropBox, Rotate, and UserUnit on a shared parent instead of repeating them on every page. This tool follows the page tree and reports the object that supplied each inherited value. BleedBox, TrimBox, and ArtBox are checked on the page itself and otherwise shown as CropBox defaults.
UserUnit scales default PDF user-space units, whose normal size is 1/72 inch. The coordinate column is normalized to physical points after UserUnit is applied. Display width and height swap for pages rotated 90° or 270°.
What inconsistency warnings mean
Pages are marked inconsistent when their effective boxes, rotation, or UserUnit differ. That can be intentional—for example, a foldout or landscape insert—but it deserves review. The tool also flags CropBox outside MediaBox, BleedBox outside CropBox, TrimBox outside BleedBox or CropBox, non-right-angle rotation, and pages that explicitly carry both TrimBox and ArtBox.
Preflight boundary
This is a structural box inspector, not complete PDF/X preflight or rendering certification. It does not render artwork, inspect marks, fonts, overprint, transparency, spot colors, image resolution, output intents, ICC profiles, separations, annotations, layers, or printer-specific standards. Complex damaged PDFs and unsupported stream filters can require Acrobat Preflight, callas pdfToolbox, Ghostscript, or another full PDF engine.
Frequently asked questions
Does the PDF leave my computer?
No. The file is read by JavaScript in this browser tab. There is no upload endpoint. The selected filename and calculated dimensions are not sent to analytics.
Why does a missing TrimBox show the CropBox dimensions?
That is the PDF defaulting rule. The source column says “defaulted to CropBox” so an implicit fallback is not confused with an explicitly authored production boundary.
Can this change or repair the boxes?
No. It is deliberately read-only. Rewriting a PDF safely requires preserving cross-references, streams, signatures, metadata, and conformance details beyond this static inspector.
Why is an encrypted PDF rejected?
Even a PDF that opens without prompting can have an encryption dictionary. This lightweight parser does not decrypt content or bypass document security.
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