How to crop a PDF, and what cropping really hides
· 5 minute read
Trim margins and scanner borders off PDF pages. How cropping works in points, why it hides rather than deletes, and what to use when something must go.
Pages come with more frame than you want. A scanner leaves a grey border. A slide exported to PDF has wide margins that make the text look small on a phone. A page copied out of a report still has a header you do not want to share. Cropping changes how much of the page is shown.
How cropping works
Every PDF page has a visible area, a rectangle that says which part of the page a viewer should display. Cropping moves the edges of that rectangle inwards. Everything outside is no longer shown, and everything inside is exactly as it was.
The amounts are measured in points. There are 72 points to an inch, so 36 points is half an inch, which is about 1.3 centimetres. A margin of 18 points is a quarter of an inch. If a tool asks for numbers instead of a drag handle, start with a small value and increase it until the page looks right.
Common uses
- Removing the black or grey border from a scanned page.
- Cutting wide margins from a slide deck so it reads better on a small screen.
- Tightening a page before it goes on an e-reader, where a smaller frame means larger text.
- Trimming a header, footer or side note you do not want to circulate.
The important caveat: cropping hides, it does not delete
The area you crop away is still inside the file. A viewer does not show it, but it has not been erased, and some programs can reveal it by resetting the page boundaries. That is perfectly fine for appearance and wrong for confidentiality.
If you crop a page to remove a name, an address or a figure, and then send the file, you may be sending the name, address or figure. Where something has to be gone, use Redact, which deletes the text from the page, not just from view.
Cropping a range of pages
The same trim usually applies to every page you select. If the front pages need a different crop from the rest, do it in separate runs with a page range, and merge afterwards if you want one file. A page that is too small to lose the amount you asked for should be left alone, and a good tool says so.
Cropping a scan
If you still have the original photograph, crop that before you make the PDF. Trimming a picture is lossless to the extent your editor allows, and gives a cleaner result. If you only have the PDF, trimming the page frame is the quick fix. Photographs gathered into a document with JPG to PDF can be set to fit a standard page, which hides some of the border problem.
Check the edges
After cropping, look at the page edges for text that has been clipped. A line of print that starts right at the margin is the first thing to be cut. If anything is touching the edge, go back and trim a little less.
Tools mentioned
- Crop PDF — Trim the margins so the page shows only what you want.
- Redact — Take words out of the file, not just paint over them.
- JPG to PDF — Photos and scans gathered into one document, each page its image.