Crop PDF & Trim Margins

What cropping a PDF actually changes

Every PDF page carries two rectangles: the media box, which is the physical sheet, and the crop box, which is the region a viewer displays and prints. Cropping sets a smaller crop box — and, if you leave the second option ticked, a matching media box so the page is genuinely smaller in every application. Nothing inside the page is re-rendered or re-compressed, which is why a cropped PDF keeps its text selectable, its vectors sharp and its images at full resolution.

Auto-trim for scanned documents

Scans and phone photos of documents almost always arrive with a thick white or grey border, sometimes with a dark edge where the lid did not close, and often sideways — if yours are, straighten them in Rotate PDF before cropping. Auto-trim renders the page, walks the pixels, and finds the bounding box of everything that is not blank — then pulls the margins in to just outside it, plus whatever padding you ask for. Two controls make it work on real-world scans: padding keeps a few millimetres of breathing room around the text, and tolerance decides how far from pure white still counts as blank, which is what lets it ignore the grey cast of an old photocopy.

Per-page trimming for book scans

When a book is scanned page by page, the text block drifts: one page sits high, the next leans left. A single crop box then cuts one page perfectly and clips the next. Turn on per-page auto-trim and every page is measured individually before the file is written, so each one keeps its own margins. It takes longer on a long document because every page has to be rendered once, but it is the difference between a tidy e-reader file and a frustrating one.

Reading PDFs on a phone or e-reader

This is the most common reason people crop: an A4 research paper with 25 mm margins wastes almost a third of a small screen. Trimming the white space makes the text noticeably bigger on a Kindle, a tablet or a phone without changing a single glyph. Crop once, and every reader app benefits, because you are changing the page box rather than zooming.

Printing and binding

Cropping is also a pre-press step. You might trim a bleed area before sending pages to a printer, cut the crop marks off a proof, remove a header band that an HTML to PDF conversion added, or standardise a set of pages that came from different sources so they all print at the same size. Because the crop is applied per page with odd/even and range options, a double-sided document can have different treatment on each side.

How much can you safely crop?

Leave a few millimetres. Trimming right up to the ink looks tidy on screen but causes two problems later: printers cannot print to the very edge of a sheet, so a hard-trimmed page gets clipped or re-scaled to fit, and OCR engines read a text block noticeably better when there is clear space around it — characters touching the page edge are the ones most often misread. The auto-trim padding setting exists for exactly this; 2–3 mm is a good default, and 5 mm if the file is heading for a printer. For screen reading only, you can trim tighter.

Why a cropped scan can still look crooked

Cropping changes the page boundary, not the content inside it. If a scan went through the feeder at a slight angle, the text stays at that angle and a straight crop box simply frames a tilted block. Auto-trim handles this as well as it can — it measures the bounding box of everything on the page, so a tilted block produces slightly wider margins than a straight one — but the fix for real skew is to rescan or deskew first. What cropping does solve completely is the uniform white or grey border, the dark strip where the lid did not close, and pages that were scanned at A4 when the document was A5.

Cropping is not redaction

One important caveat: hidden is not deleted. Content outside the crop box stays inside the file and can be recovered by anyone who resets the page boxes. If your goal is to remove confidential information rather than tidy a layout, use a tool that actually deletes it — see the PDF Redaction tool — and check the result before sharing.

Privacy & security

The document is opened, measured and re-saved with JavaScript in your own browser. No copy is uploaded, nothing is stored on a server, and the page keeps nothing after you close the tab — which matters when the thing you are cropping is a bank statement, an ID scan or a signed contract.