Cropping a PDF without losing text

Hidden, not deleted

A crop box is geometry: four numbers describing the visible rectangle. The content underneath stays in the file, which is why cropping a page does not reduce its size much, and why text outside the visible area can still be found by a search.

That is fine for layout and dangerous for secrecy. If you crop a page to remove a phone number or an account reference, the characters are still in the document and can be recovered.

Cropping is not redaction

Redaction removes content and leaves a mark where it was. Cropping hides it and hopes nobody looks. For a legal filing, a medical record or anything that will be published, the difference matters a great deal.

The practical test: if the document were opened by someone who knew what to look for, would the hidden content be recoverable? If yes, it needs redacting, not cropping.

Margins in millimetres

Crop margins are measured from each edge of the page, in millimetres, and they cannot enlarge the page. Ten millimetres is a little under half an inch; trimming 15 mm from each side of A4 leaves a page about 180 mm wide.

For a scanned page with a wide white border, the usual job is 10–20 mm on each side. For a screenshot-heavy page with almost no margin, a crop of 2–5 mm is enough.

Applying it to the right pages

Mixed documents need different treatment per page: a cover sheet may need no crop while the body pages need 15 mm. Apply a crop to all pages only when you have checked that they share the same layout.

• All pages: same layout throughout.
• Odd or even pages: mirrored margins in a bound document.
• This page: anything that differs.