What cropping does to the file
Every PDF page carries a set of boxes that describe its geometry. Here, only the crop box matters: it says what part of the page a reader should show you.
Cropping changes that boundary. It does not cut anything out of the file. The content outside the new edge is still sitting there, hidden rather than removed, and that has two consequences.
The good one: nothing is destroyed, nothing is redrawn, text stays selectable and vector drawings stay sharp at any zoom. The file barely changes size because nothing was thrown away.
The one to be careful about: it is not a way to hide something confidential. If a name or a figure is in the margin you are cropping off, it is still in the document and a determined reader can recover it. For that you want redaction, which is a different job with different rules.
How this tool works
Cropping a PDF does not remove anything. It sets a rectangle on each page saying which part should be displayed, and everything outside it is still in the file, just not shown.
That is worth knowing for two reasons. It means cropping is reversible and costs no quality, because nothing is redrawn or thrown away. And it means cropping is not redaction: anything you crop off can be recovered by resetting the box, so it is no way to remove confidential margins from a document you are sending out.
Why both boxes get set
A page has a crop box and a media box. Most readers honour the crop box, so setting that alone looks completely correct on screen. Plenty of printers and a fair amount of older software use the media box instead.
Set only the crop box and you get the classic result: it looks perfect on your monitor, you send it to be printed, and back comes the full original page with every margin you thought you had removed. So this sets both to the same thing, and the finished page really is the size it says it is.
What people are usually cropping
- The black border off a scan. A document scanned slightly small leaves a dark frame that wastes toner and looks careless.
- Enormous margins on a report. A document laid out for binding has 30mm down one side that nothing will ever be printed in.
- A header or footer from another system. A portal stamps a URL and a timestamp across the top of everything it exports.
- Whitespace around a drawing, so the drawing itself fills the sheet when it is printed or dropped into another document.
- Making a document fit a smaller sheet without scaling the content down and making the text harder to read.
Getting the edges the right way round
This trips up more tools than you would expect, because a PDF measures from the bottom left corner rather than the top left like almost everything else in computing. Confuse the two and a request to trim the footer takes the header off instead, which looks nearly right and is completely wrong.
The preview exists for exactly that reason. It draws the page to scale with the area you are keeping marked on it, updating as you type, so you can see which edge is going before you commit to anything.
There is also a floor. Ask for more than the page has and it holds at the smallest crop that still leaves something usable, and says it has done so, rather than writing a file with a zero sized page that opens completely blank.
Millimetres, not percentages
The measurements are in millimetres because that is what people can check. If a scan has a 12mm black edge, you can hold a ruler against the printout and type 12. A percentage means working out what percentage of 297mm your 12mm is, which is a step nobody needs.
The finished page size is shown in millimetres too, so you know what you are ending up with: useful when the result has to fit a sleeve, a binder or a specific paper size.
A crop hides, and an upload does not even do that
No account, no email, no size limit and no watermark. The document is opened, changed and saved by your own browser, and nothing leaves the page.
Worth being clear about what a crop is, because the privacy of the tool is not the privacy of the result. Cropping changes what is displayed. It does not reliably remove what sits outside the new box, so a cropped page can still carry the text you cropped away. Where the point is to remove something rather than to tidy the margins, redact it instead.
Common questions
How do I crop the margins off a PDF?
Type how many millimetres to take off each edge and it shows you the result drawn to scale before anything changes. Ten millimetres all round handles most oversized margins, and the preview means you are not guessing.
Does cropping actually delete the content outside the box?
No. Cropping sets the visible area of the page: the content outside it is still in the file, and somebody who knows how can bring it back. It is a tidying operation, not a way to remove something confidential.
Will it still print properly?
Yes. Both the crop box and the media box are set to the same thing, so readers and printers agree on the page size. Some tools only set the crop box, which looks right on screen and then prints the full original page with everything you cropped still on it.
Can I crop just one page?
Yes. Choose "just some" and type the page numbers. Useful when one page came out of a different scanner, or a single landscape drawing is sitting in a portrait document.
Will the text still be selectable?
Yes. Nothing is redrawn or rasterised. The page content is untouched and only the visible boundary changes, so text stays text and vector drawings stay sharp at any zoom.