How the crop works
You give four numbers in millimetres, one per edge, and every page in the document is trimmed by that much. The change is made by moving the crop box inwards, which is the honest way to crop a PDF: no page is re-rendered and nothing is discarded, viewers and printers simply show the smaller area you asked for.
That keeps the result clean. Text stays selectable, images keep their original resolution, links keep working and the file size barely moves. Processing runs on our own server with pdf-lib, the result is free of watermarks, and you download it as your-name-cropped.pdf. If the numbers you enter would leave nothing of a page, the job stops and tells you which page number is the problem.
Cropping is not redaction
Because the trimmed area is still inside the file, a crop is reversible: reset the crop box to the full page and the margins come back. That is useful when you only want a tidier reading view, and it is exactly wrong when the point is confidentiality. To make content genuinely disappear from a document, use Redact PDF, which flattens the page and removes the text underneath the marked areas.
Typical cropping jobs
- Scanner borders. Cut the grey or black frame that a flatbed scanner leaves around the sheet.
- E-books on small screens. Trim wide white margins so the text fills a phone or e-reader page.
- Headers and footers. Push a running header or a footer band outside the printable area.
- Slide handouts. Remove empty space around exported slides before printing them.
Cropping pairs well with the rest of the cleanup. Straighten sideways scans first with Rotate PDF, crop only part of a document by taking it out with Split PDF and putting it back with Merge PDF, or run Compress PDF if the scan is heavy.