How to Crop PDF Margins, and What Cropping Never Does
A scan comes back with two inches of grey around every page. A report has a running header you would rather not print. A book scan has the shadow of the opposite page down one edge.
Cropping fixes all three, and it is one of the easiest operations in this whole toolbox. It is also the one most often expected to do something it does not do — so before the steps, the single most useful thing to know about it.
Cropping hides. It does not delete.
A PDF page carries two rectangles that matter here.
The MediaBox is the sheet: the full physical page, everything the document was built on. The CropBox is the window: the region a viewer or printer actually shows. When you crop, you are moving the window. You are not cutting the sheet.
The content outside that window is still in the file. Every word, every part of the image. It is not displayed, it is not printed, and it comes straight back the moment anyone widens the crop box again — which is a thing any PDF editor can do in about three seconds.
This has two consequences, and both surprise people.
It will not make your file smaller
If you are cropping to get a file under an email limit, stop — it does not work, and the arithmetic says why. The bytes are in the content, and the content is all still there. You have added two numbers to the page dictionary and removed nothing at all.
Measured on a five-page document with content running to all four edges, cropping a full inch off every side:
| file size | |
|---|---|
| original | 5.4 KB |
| cropped, page size preserved | 5.5 KB |
| cropped, page resized | 5.5 KB |
Cropping made it bigger — by about 140 bytes, the cost of writing the new box entries. That is the honest result, and it holds regardless of how much you trim.
If size is the actual problem, the causes and the real fixes are in why is my PDF so large, and the operation you want is Compress PDF.
It is not redaction
This one matters more.
Cropping a bank account number out of the margin does not remove the bank account number. It hides it behind a window, in a file you are about to send someone. Anyone who opens that file in an editor and resets the crop box sees it, and so does anything that reads the text layer directly — text selection does not respect the crop box the way your eyes do.
If something must not reach the recipient, remove the whole page. That is a real operation: Delete PDF Pages builds a new document from the pages you kept, and the page you dropped is not copied into it. See how to remove pages from a PDF.
No tool on this site claims to redact, and cropping is not a quiet exception to that.
The two crop modes
Both modes move the window. The difference is whether the sheet moves with it.
Preserve page size (hide the cropped area). Sets the CropBox and leaves the MediaBox alone. The page’s declared dimensions are unchanged; only the visible region shrinks. This is the safer default, because nothing about the page geometry is altered — reset the crop and you are exactly back where you started.
Resize the page to the crop bounds. Sets both boxes. The page’s declared size becomes the crop rectangle. Use this when you want genuinely smaller pages: fitting an A4 scan onto a smaller trim size, or making a document whose pages are all the same size after cropping different scans by different amounts.
The practical test: will anything downstream care about the page dimensions? A printer will. A layout program placing these pages will. A person reading on screen will not. If something downstream reads page size, resize; otherwise preserve.
Crop settings are never applied silently to pages you did not pick. You choose current page, selected pages, or all pages, every time — because a document of mixed scans usually needs different margins on different pages, and one global crop applied by surprise is how a figure loses its caption.
Cropping, step by step
- Open Crop PDF and choose your file. It stays on your device.
- Set margins for each side, or drag the crop box on the preview.
- Pick a mode: preserve page size, or resize to the crop bounds.
- Pick which pages it applies to.
- Export.
If your margins would consume the whole page, you get an error saying so rather than a document of blank sheets.
Margins are in points, and a point is 1/72 inch
The numbers you type are PDF points. Seventy-two of them make an inch, which makes the conversions easy to do in your head:
| trim | points |
|---|---|
| 1/4 inch (6 mm) | 18 |
| 1/2 inch (13 mm) | 36 |
| 1 inch (25 mm) | 72 |
| 1.5 inch (38 mm) | 108 |
A US Letter page is 612 × 792 points. A4 is 595 × 842. Those two numbers are worth remembering, because they tell you immediately whether a margin is plausible: trimming 100 points off each side of a 612-point-wide page leaves 412 points of content, which is fine. Trimming 300 leaves 12, which is not.
Measure once instead of guessing three times
The reliable method takes ten seconds and beats iterating. Note where the content actually starts relative to the page edge — most viewers show cursor coordinates, and the preview here shows the crop rectangle as you drag it. Then subtract a few points for safety and use that number.
Guessing tends to go one of two ways: too timid, so you crop three times, or too aggressive, so you clip a page number off the bottom and do not notice until it is printed. Start conservative. Your original is untouched, so a second pass costs nothing but a minute.
What to watch for afterwards
Check the widest page, not the first one. Documents are rarely uniform. A landscape table or a fold-out figure sits closer to the edge than body text does, and a crop that flatters page 1 can behead page 14. Skim the whole document at thumbnail size after cropping — outliers are obvious at that scale.
Check the bottom edge specifically. Page numbers, footnotes, and footer rules live there, closer to the trim than anything else on the page. If a crop is going to cut something, this is what it cuts.
Print one page if the output is for print. Screen and paper disagree about edges more often than you would like, and printers have their own unprintable margin on top of your crop.
Order of operations
Cropping interacts with two other operations, and the order is not arbitrary.
Rotate first, then crop. Crop margins are measured from the page edges as the page is currently oriented. Crop a sideways scan and then rotate it upright, and your “top” margin is now down one side. Straighten first — how to rotate PDF pages covers doing it properly, including why a page can look right and still be rotated wrong.
Crop before OCR, not after. Text recognition works better on a clean page, and scanner edge shadows are exactly the noise that produces garbage characters. See how OCR makes scanned PDFs searchable.
Crop before assembling a bundle. Get every page looking right, then combine and number. The reasoning is the same one behind preparing a PDF bundle for submission: fix the pages, then fix the document.
Where this sits in the format
Page boundary boxes are defined by ISO 32000-2, the standard behind PDF, which specifies the MediaBox, CropBox, and several other boxes used by printers and prepress tools. The PDF Association publishes readable reference material on that structure if you want to understand what a viewer is actually reading.
Two of those other boxes explain a question that comes up with print work. The TrimBox marks where the finished page is meant to be cut, and the BleedBox marks how far ink should run past that cut so a slight misalignment on the guillotine leaves no white sliver. A commercial printer reads those, not your CropBox — which is why a file that looks correctly cropped on screen can still come back from a print shop trimmed somewhere else entirely.
The practical takeaway from the spec is the same as the practical takeaway from the tool: these boxes describe how a page is presented, not what a page contains. Cropping is a presentation change. Treat it as one, and it will never surprise you.
Keep the original
Cropping is reversible in principle — the content is still there — but only if you know the original numbers, and you will not. Keep the file you started from until the cropped copy is checked and sent.
Everything here runs in your browser, so the document never leaves your device to be cropped. Why that matters is covered in how browser-based PDF processing protects your privacy.