Scanned documents come back with grey margins. Reports include header and footer space you don't want printed. Slides exported to PDF have black borders. Cropping a PDF removes the parts you don't need — but with a twist most people don't realise. Done wrong, the cropped content still lives in the file. Done right, you get a clean, smaller, safer PDF.
What "cropping" actually means in a PDF
There are two ways a PDF tool can crop a page:
- Visible crop (CropBox change). The tool tells viewers "only show this rectangle." The hidden content remains inside the file. Anyone who opens the file in another tool and removes the crop can see what was hidden. This is the default in most tools, including Adobe Acrobat.
- True crop (rasterise or re-render). The tool actually removes the parts outside the crop rectangle and saves a new, smaller page.
This distinction matters enormously for redaction. If you are cropping a contract to hide a salary line, a visible crop is not enough — the salary is still in the file. Use redaction for hiding sensitive content; use cropping for removing unwanted whitespace.
Method 1: Browser-based crop
A browser tool lets you draw a rectangle on the page and apply the same crop to all pages, odd pages, even pages, or a custom range. Docento.app does this in your browser without uploading the file — important when the document contains anything you would not want sent through a third party.
Useful options to look for:
- Apply to range: cropping just the cover page is rare; usually you want pages 2-N.
- Auto-detect content: snaps the crop rectangle to the page's actual content, ignoring whitespace. Saves time on long documents.
- True crop output: confirms hidden content is removed, not just hidden.
Method 2: macOS Preview
Preview can crop one page at a time: select with the rectangular tool, then Tools → Crop. Apply once and the change persists. It uses CropBox, so hidden content remains; fine for tidying, not safe for sensitive data.
Method 3: Command line for batch cropping
For consistent crops across many files (every monthly statement has the same blank header), the command line is faster:
- qpdf with
--pagesdoes selective extraction but not cropping directly. - pdfcrop (TeX Live): auto-detects bounding boxes and crops to content. Run
pdfcrop input.pdf output.pdfand it usually does the right thing. - Ghostscript: full control with
-sPageList=and-c "[/CropBox [...]" def. Verbose but powerful.
Pair these with our batch processing guide for repeatable workflows.
Special case: cropping scanned PDFs
Scans often have grey borders, the edge of the scanner platen, or even fingertips at the corners. Cropping is the right fix, but two things to watch for:
- If the scan was done at an angle, cropping straight lines won't help — you need a deskew step first.
- If the document is text-heavy and you plan to OCR it, crop before OCR. Cleaner edges produce cleaner text. See our OCR guide.
Cropping for printing vs cropping for screen
The right crop depends on the destination:
- For screen reading: crop generously to maximise visible content. Phones and tablets have limited screen real estate.
- For printing: keep at least 5 mm of margin around content. Many home printers can't print to the very edge and will silently scale the document, undoing your careful crop.
- For booklet printing: leave extra margin on the binding side. See how to print a booklet from a PDF.
Cropping vs resizing
These get confused. Cropping removes content from the edges. Resizing changes the page dimensions, scaling content up or down to fit. If your goal is "fit this A4 page into a Letter slot," that's resizing, not cropping. Most browser tools have separate buttons for each — make sure you pick the right one.
Final checks after cropping
- Open the file in a different reader to confirm the crop survives. CropBox changes can occasionally disappear in tools that ignore non-default page boxes.
- Check page numbering is still correct. Cropping doesn't change page count, but if you trimmed page numbers off the bottom, you may want to re-add them.
- Compare file sizes. A true crop should produce a noticeably smaller file. If the file size is the same, you almost certainly only changed the CropBox.
Conclusion
Cropping is a small tool with two modes that behave very differently. Use a true-crop tool when sensitive content sits at the edges. Use a visible crop when you just want a tidier presentation. Docento.app supports both modes in the browser, and when you are done, our guide on reducing file size covers the next step if the file still feels too big.