Crop PDF Pages by Trimming Millimetres From Each Edge

About the PDF Cropper

Four number fields, one per edge, each starting at 10 millimetres. Enter the amount to remove from each side and the crop is applied to every page in the document. The measurements are in millimetres rather than points because the numbers you want to remove usually come from looking at a printed sheet with a ruler, not from a page-description specification.

A guard stops you from destroying the document: if the values you enter would leave a page smaller than about half an inch in either direction, the tool refuses and tells you rather than producing something unusable. Otherwise there is no upper constraint — you can trim aggressively when a scan has a wide black frame around it.

Key Features

• Independent control of each side: Top, right, bottom and left are separate fields, so an asymmetric crop for a scanned page with a shadow down one edge is straightforward.
• Millimetre input: Values map directly to what you would measure on paper, and are converted to points internally at the correct ratio.
• Both page boxes are set: The crop box and the media box are updated together, which is what makes the crop hold consistently across different PDF readers rather than displaying one way and printing another.
• Applied across the document: One set of values crops every page, which suits scans and exports where the same unwanted border appears throughout.
• The content is never re-rendered: This changes the page geometry only, so text remains selectable and images keep their original resolution.
• No transfer for a geometric edit: Trimming is done by pdf-lib in the browser from code on this domain, so a document does not travel in order to have its edges adjusted.

How to Use the PDF Cropper

1. Add the PDF whose pages need trimming.
2. Enter how many millimetres to remove from the top, right, bottom and left — any of them can be zero.
3. Press Crop PDF.
4. Download the file, saved with -cropped appended, and check a page before committing to the values.

How It Works

For each page the tool converts your millimetre figures to points and sets both the crop box and the media box to the remaining rectangle, offsetting the origin by the left and bottom trims because PDF coordinates start at the bottom-left corner of the page rather than the top-left.

Here is the part that matters most, and it is the opposite of what most people assume. Cropping a PDF does not delete anything. It moves the window through which the page is viewed. The content outside that window is still in the file, and anyone who resets the page boxes in a PDF editor can see it again in full. This is entirely fine for tidying scanner borders or removing crop marks, and it is completely unsuitable for hiding information. If something must be gone, it has to be removed from the content rather than cropped out of view.

The second limitation is uniformity: the same trim is applied to every page, and there is no page-by-page adjustment and no automatic margin detection. A document whose scans drifted as the pages fed through will need the trim set conservatively enough to suit the worst page.

When You Need It

A surveyor scans handwritten site notes on a flatbed and every page comes back with a two-centimetre black band down one side where the lid did not close flat. Trimming that band off makes the notes legible on screen and stops the band swallowing toner if they are ever printed. The notes are produced under a client instruction with confidentiality attached, so a crop that happens locally avoids putting a client's site details through a conversion service.

Someone reading a dense report on a phone during a commute finds the type unreadably small because a third of each page is margin. Cropping the margin away lets the reader zoom to the text width and get noticeably larger type, turning an unreadable PDF into something that works on a small screen.