You've got a PDF with an inch of white space on every side, so the text is tiny on a phone or e-reader. Or a scan with a grey scanner lid border round the edge. Or a journal article where you only want the column of text and none of the page furniture.
Cropping fixes all three. Crop PDF can find the white margins for you, or you drag a box over the page and keep what's inside it. Before you use it on anything sensitive, though, it's worth knowing what a crop actually does to the file, because it isn't what most people expect.
A crop hides the edges, it doesn't cut them off
A PDF page has more than one size. The MediaBox is the full sheet, the physical paper the page was made for. The CropBox is the part of that sheet a viewer should show. Most of the time they're the same, so nobody notices there are two.
When you crop a page, Crop PDF writes a smaller CropBox. Every viewer (Adobe Acrobat Reader, Preview on a Mac, Chrome, your phone) then shows only that area. The text, images and drawings outside it are still in the file, untouched. That's why cropping is instant, why there's no quality loss, and why the file usually stays about the same size.
It's also why you can undo it later. Any tool that edits page boxes can set the CropBox back to the full page and everything reappears.
That last point matters. If you crop away a name, an account number or a note in the margin, it's hidden, not gone. Someone with the right software can bring it back. To actually remove something, use Redact PDF, and read how to redact a PDF properly first.
The three ways to start
After you add your file, Crop PDF asks you to "Choose an option":
- "Automatic" finds the white margins that every page has in common and cuts those. All pages get the same crop, so no page loses content.
- "Automatic maximum crop" trims each page's white margins on its own. Each page is cropped as tightly as it can be, which means pages can end up different sizes.
- "Preview pages & select" opens a preview where you set the crop yourself.
The two automatic options crop the file as soon as you click "Continue". For a clean text document, "Automatic" is usually all you need. I'd avoid "Automatic maximum crop" for anything you'll read as a document, since a short last page of a chapter shrinks to a little strip and the zoom jumps around as you scroll. It's handy for figures and diagrams, where tight edges are the whole point.
How does it decide what's white? It renders each page and looks for any pixel that isn't close to pure white, then leaves 3 points (about 1 mm) of breathing room round the content it finds. That works well on PDFs made from Word or a web page. It works less well on scans, where the "white" paper is often light grey and the scanner adds a dark edge. If it says "No white margins were found. Set the crop area by hand.", that's usually why.
Cropping by hand
- Open Crop PDF and add your PDF.
- Choose "Preview pages & select" and click "Continue".
- Pick a "Preview mode" in the settings bar: "Blended", "Page by page" or "Odd & even".
- Drag the edges or corners of the blue box, or drag inside it to move it. The darkened area is what gets cut.
- For exact numbers, type them into "Top", "Bottom", "Left", "Right", "Width" and "Height", in inch, cm, mm or points.
- Click "Crop PDF" and download the result, saved as cropped-yourfile.pdf.
"Blended" is the clever one. It draws the pages on top of each other (up to 24 of them in the preview), so you can see every place content appears on any page. Set the box so nothing in the blend is cut and you know the crop is safe for the whole document. "Auto-trim white margins" does the same calculation for you.
"Page by page" gives each page its own crop. Use "Prev" and "Next" to move through, or "Auto-trim this page" and "Auto-trim every page". Pages you don't touch are left as they are.
"Odd & even" exists for book scans. When you scan an open book, the inner margin (the gutter by the spine) is on the right of odd pages and the left of even pages, so one crop never fits both. Set the "Odd pages" crop, switch to "Even pages", set that one, and you're done.
Under "More options", "Pages" limits the crop to certain pages, for example "1-5, 8" or "odd". Leave it empty for all of them.
When to tick "Also shrink page size"
By default only the CropBox changes. That's fine for reading on screen. Printing is less predictable, because some print paths and some apps look at the MediaBox (the full sheet) instead.
"Also shrink page size" sets the MediaBox to the crop as well, so the cropped area becomes the page size as far as printers and other software are concerned. The content outside is still hidden rather than deleted, so the privacy point above still applies. Tick it if you're sending the file to a print shop, or if the next tool in your chain keeps showing the old margins.
What cropping won't do for you
It won't make the page a standard paper size. Crop a Letter page and you get an odd size like 6.8 x 9.4 inches, which a printer will either scale up or print with white borders anyway. If you want the content to fill A4 or Letter again, run the cropped file through Resize PDF with "Scale to fit". That pair (crop, then resize) is the standard trick for making small print bigger on paper.
It won't straighten a crooked scan either. A box drawn round a tilted page either clips the corners or leaves wedges of border. Straighten it with Deskew PDF first and crop afterwards. The guide on straightening a crooked scanned PDF covers that.
And it won't shrink the file. The hidden content is still there. If size is the problem, that's Compress PDF.
Check the last page
Automatic crops are calculated from what's on the pages, so one odd page can throw them off. A page with a full-width table or a landscape chart has no white margin on its sides, and "Automatic" will then crop the sides of every page by only as much as that page allows, often nothing at all. If the result looks barely cropped, switch to "Page by page" and look for the page that's holding it back. Then scroll through the downloaded file to the very end, because the page most likely to be clipped is the one you didn't look at.
Also useful: Resize PDF · Redact PDF
