When you need to crop a PDF
Cropping cuts away the edges of a page so only the useful part remains. Common reasons:
- Scans with wide grey or black borders around the paper
- Slides exported to PDF with lots of empty space, which waste paper when printed
- Academic papers you want to read on a phone or e-reader without the wide margins
- One figure or table you need to cut out of a page and share on its own
- Printer marks and bleed around a print-ready file
How to crop a PDF
- Choose your PDF. The first page appears with a blue crop box around it.
- Set the crop in one of three ways:
- drag the round corner handles, or drag inside the box to move it
- type exact margins in millimetres (top, bottom, left, right)
- click a preset (trim 5, 10 or 20 mm) or Auto-trim white margins
- Pick the pages: all of them, only the page on screen, or a list such as “1-3, 6”. Use the arrows under the preview to check other pages.
- Click Crop and download. The file name ends in “-cropped”.
How auto-trim works
Auto-trim draws each chosen page at a small size and scans it pixel by pixel for anything darker than near-white. The smallest box that contains all of that content becomes the crop, plus a 6-point (about 2 mm) border so letters are not cut too tightly. Every page gets its own box, so a scan where the paper sits in a different place on each page still comes out neat.
Auto-trim works best on clean white pages. Coffee stains, dark scanner edges or page numbers in the far corner count as content, so the box will reach them. In that case drag the box or type margins instead.
Millimetres, points and inches
PDF pages are measured in points: 72 points make one inch, and one millimetre is about 2.83 points. The tool shows millimetres because that is what most people measure with a ruler.
| Paper | Size in mm | Size in points |
|---|---|---|
| A4 | 210 × 297 | 595 × 842 |
| US Letter | 216 × 279 | 612 × 792 |
| A5 | 148 × 210 | 420 × 595 |
Example: you want to cut an A4 scan down to the 180 × 260 mm area where the text sits. That means 15 mm off each side and 18.5 mm off the top and bottom. Type 15, 15, 18.5 and 18.5, and the label under the preview confirms “keeps 180 × 260 mm”.
What cropping does inside the file
A PDF page has several “boxes”. The MediaBox is the paper size and the CropBox is the part viewers display. This tool sets both to your rectangle and removes the print-production boxes (bleed, trim and art boxes), so every viewer and printer agrees on the new size.
The content outside the box is hidden, not deleted. It stays in the file, and that is true of every PDF cropping tool. It means you can never lose content by cropping, but it also means cropping is not a privacy tool. To make text truly unrecoverable, use Redact PDF. It also means file size barely changes. Run Compress PDF afterwards if size matters.
This cropper vs typical online croppers
| This tool | Typical online croppers | |
|---|---|---|
| File uploaded | No, stays on your device | Yes |
| Crop one page differently from others | Yes | Not always |
| Auto-detect white margins | Yes, per page | Sometimes |
| Exact sizes in mm | Yes | Rarely |
| Limits or sign-up | None | Often on free plans |
Tips
- Rotate first. If pages are sideways, fix them with Rotate PDF before cropping, so “top” means the top you see.
- Crop to a single figure. Choose “This page”, drag the box tightly around the figure, then use Extract PDF Pages to save just that page.
- Reading on a phone? Auto-trim an academic paper. The text gets noticeably larger on a small screen.