A PDF page has two boundaries, and cropping only moves one of them
Every PDF page actually carries multiple boxes defining its geometry, but the two that matter here are the media box and the crop box. The media box is the page's full physical canvas — everything that was ever drawn on it. The crop box is a separate, smaller (or equal) rectangle that tells a viewer: only show what falls inside this region. Content outside the crop box still exists in the file's underlying data; it's simply not rendered by compliant viewers.
This is the single most important thing to understand before using this tool: setting margins here moves the crop box, not the media box. The PDF's actual content — text, images, everything — is untouched. What changes is what a viewer chooses to display.
PDF points, and why 36 isn't an arbitrary number
This tool asks for margins in PDF points, the native unit PDF geometry is defined in. One point equals 1/72 inch — a unit inherited from print typography, where 72 points to the inch made font-size math convenient. That's why 36 points equals exactly half an inch (36 ÷ 72 = 0.5): it's a clean fraction in the units PDFs actually use internally, even though it looks like an odd number if you're thinking in inches or centimeters first.
Knowing your page's total dimensions in points is what makes entering sensible margins possible: A4 pages measure 595 × 842 points, and US Letter measures 612 × 792 points. A one-inch margin on all sides of a US Letter page means entering 72 points for top, bottom, left, and right — leaving a crop box of 612 − 144 = 468 points wide by 792 − 144 = 648 points tall.
Common page sizes in points
| Page size | Width (pt) | Height (pt) | 1-inch margin all sides leaves |
|---|---|---|---|
| US Letter | 612 | 792 | 468 × 648 pt |
| A4 | 595 | 842 | 451 × 698 pt |
| Legal | 612 | 1008 | 468 × 864 pt |
Cropping your PDF
Drop a PDF onto the zone.
Enter top/bottom/left/right margins in PDF points (36 pt = 0.5 inch).
Click Crop & download — the crop box is applied to every page.
Why cropping doesn't delete anything, and when that matters
The distinction between hiding and deleting isn't a technical footnote — it has real consequences. Because the underlying content stays in the file, someone with the right software can adjust the crop box back to the full media box and see everything that was originally there. If you're trying to visually trim excess whitespace or a scanned page's dark border for a cleaner-looking document, cropping is exactly the right tool. If you're trying to remove sensitive content — a name, a signature, a confidential paragraph — from a document before sharing it, cropping gives a false sense of security: the data is still inside the PDF file itself, just outside the currently visible region.
Why the same margins apply to every page
This tool applies one set of top/bottom/left/right values across the entire document rather than offering per-page control, which keeps the workflow simple for the common case: trimming a consistent excess margin — a scanner's dark border, an overly generous print margin — that's the same on every page. If your document genuinely needs different crop regions on different pages (a mixed batch of scans at different sizes, for instance), the practical path is to split the document into the pages that need different treatment first with Extract PDF Pages, crop each group separately with its own margin values, then recombine if needed.
Getting the margins right without guessing
Since the crop box is defined relative to the page's own dimensions, the fastest way to get accurate margins is to know your source page size first — check whether you're working with A4, Letter, or something else — then compute the margin in points using the 72-points-per-inch conversion. If you're cropping to remove an inconsistent border (common with scanned documents where the scanner captured extra background), it's worth measuring the widest offending margin across a few representative pages before applying one crop value to all of them, since the same margin applied uniformly will either under-trim the worst pages or over-trim the cleanest ones.
Common mistakes
Using cropping as a substitute for redaction — hidden content is still present in the file's data and can be revealed by adjusting the crop box back.
Entering margin values in inches or millimeters by mistake — this tool expects PDF points specifically, and 1 inch is 72 points, not 1.
Applying one aggressive margin to a batch of pages with inconsistent original margins, over-cropping some pages while barely trimming others.
Expecting different pages to get different crop values in a single pass — this tool applies one set of margins uniformly across the whole document by design.
Real use cases
Trimming a scanner's dark border or shadow margin from every page of a scanned document at once.
Tightening excess whitespace around a PDF exported from a slide deck or design tool before printing.
Removing a wide, unused margin from a legal or academic document to fit more visible content per page in a viewer.
Preparing a document's visible area to match a specific print or display aspect ratio before further processing with the PDF Page Resizer.
Frequently asked questions
Q: Is the cropped content deleted?
A: No. The crop box only hides content outside it — the underlying data remains in the file. For true removal, use the Redact PDF tool or a desktop editor.
Q: What's a PDF point?
A: 1 point equals 1/72 inch. A4 measures 595 × 842 points, and US Letter measures 612 × 792 points.
Q: Can I crop only specific pages?
A: This tool applies the same margins to every page for simplicity. For per-page cropping, extract the pages you want with Extract PDF Pages and crop them separately.
Q: Is my PDF uploaded?
A: No. Cropping runs entirely in your browser via pdf-lib.
Q: If I crop too aggressively and cut off real content, can I undo it?
A: Since the crop box only hides content rather than deleting it, running the tool again with smaller (or zero) margins on the same original file restores full visibility — as long as you kept the original, uncropped PDF.
Q: My page appears rotated after cropping — is that related?
A: No, cropping only affects the crop box boundaries, not page rotation. If you also need to fix page orientation, that's handled separately by Rotate PDF.
Crop your PDF now
Adjust your page margins with the Crop PDF tool. Need to remove whole pages instead of trimming margins? Try Delete PDF Pages. Fixing page orientation? Use Rotate PDF, or resize the page dimensions entirely with the PDF Page Resizer.
