Crop PDF Online – Trim Margins by Drawing a Box

Crop PDF pages by drawing the area you want to keep

Scanners leave wide white borders. Phone cameras leave a strip of desk. A browser's print-to-PDF leaves a line of URL and date at the top and bottom. This tool lets you crop a PDF online by drawing a rectangle over the page and keeping what is inside it. You can drag the box, pull its corners, move through the document page by page, and apply the result to one page or to all of them.

People use it to trim PDF margins before printing, to cut the black edges off a scanned certificate, to crop away a header added by a website, and to make a page fit a template without opening desktop software. It is not a page-size converter: it changes what each page shows, and the file keeps everything it had.

How to crop a PDF

1. 1
   Drop the PDF onto the box, or click it to browse. The tool takes one PDF at a time, and page 1 appears once it has been drawn.
2. 2
   A crop box starts on the page, set in from each edge. Drag anywhere on the page to draw a new box, drag inside the box to move it, and pull any of its four corners to resize it.
3. 3
   Use the Previous page and Next page arrows to look at other pages. The line above the preview reads Page 3 of 12, so you always know where you are.
4. 4
   Check the Keeping box, which reports the size of your selection as a share of the page, for example 84% wide x 84% tall.
5. 5
   In Apply the crop to, choose Every page or This page only.
6. 6
   Press Apply crop. The tool shows how many pages were cropped and the new file size. Press Download to save cropped.pdf.

What cropping does to the file

Cropping in a PDF means setting the page's crop box, a rectangle that tells viewers and printers which part of the page to show. The tool uses pdf-lib to write that rectangle onto each selected page. The page's full original area, its media box, stays as it was, and so does everything drawn on it.

That is why the trimmed edges are hidden, not deleted. Text and images outside the box are still in the file, and a PDF editor can reset the crop box and bring them back. It also explains why the file size does not shrink. In a test on a 12-page file of 12,646 bytes, cropping changed the size by 18 bytes.

Your selection is stored as fractions of the page, not screen pixels, because the preview may be any size depending on your device. The fractions are converted to points only when the file is written. A fraction survives that conversion cleanly, so the area you saw is the area you get on a phone or on a large monitor.

A worked example in points and millimetres

A4 is 595.28 by 841.89 points (210 by 297 mm), and there are 72 points to an inch. The default box keeps from 8 per cent to 92 per cent across and down, so the Keeping box reads 84% wide x 84% tall. In points, the left edge of the crop box is 0.08 x 595.28 = 47.6 and the bottom edge is 0.08 x 841.89 = 67.4 above the foot of the page. The kept area is 500.0 by 707.2 points, which is 176.4 by 249.5 mm.

A tighter crop suits a scan with only thin borders. Set the box from 5 per cent to 95 per cent across and from 4 per cent to 96 per cent down. You keep 90% wide x 92% tall. That is 535.8 by 774.5 points, or 189.0 by 273.2 mm, with a 29.8-point strip trimmed from each side and 33.7 points from the top and bottom.

The same arithmetic shows why Every page and mixed sizes behave sensibly: a fraction of an A4 page and the same fraction of an A5 page are different numbers of points, but they trim the same proportion of each sheet.

Exact margins in points

The page you use here is a visual editor, so you judge the crop by eye. If a printer or portal gave you precise numbers, use the Crop margins step in a chained workflow. It offers All sides (pt), which starts at 24, plus Top, Bottom, Left and Right, each starting at -1 meaning use the all-sides value, and a Pages list. Values are whole points, with 72 points to the inch.

On A4 the default of 24 points on every side leaves a crop box of 547.28 by 793.89 points. If the margins would leave less than 10 points in either direction, the step stops with a message that states the page size, for example 595 x 842 pt, rather than producing an empty page.

How the crop box behaves under your finger or mouse

The preview reacts to a mouse, a stylus or a touch screen, so the same page works on a phone. Dragging on empty page space starts a fresh rectangle from the point where you pressed. Dragging inside the box moves it without changing its size, and it stops at the page edge. Pulling a corner changes two sides at once, and each corner refuses to cross the opposite one: the box never gets narrower or shorter than 3 per cent of the page while you drag.

When you press Apply crop, a stricter check runs. The final area must be at least 5 per cent of the page in both directions, otherwise you are asked to drag out a larger rectangle. This guards against a stray click that would leave a page with almost nothing visible.

Trimming a scanned certificate for an upload form

Here is a typical job. You have scanned a mark sheet on A4 at 200 dpi, which makes a page image of about 1654 by 2339 pixels, and the scanner has left a grey border and a shadow along the left edge. The portal wants a clean image of the document without the desk around it.

Draw a box that follows the printed border of the sheet, with a small gap, and check Keeping. At 90% wide x 92% tall the visible area is roughly 1488 by 2152 pixels of the original scan. Apply it to Every page, download cropped.pdf, and open it to be sure no seal or signature has been clipped.

The picture inside the file is still the full scan, so its size has not moved. If the portal has a limit such as 200 KB, run the cropped file through a tool that can set a target size, because the crop alone leaves the file as big as it was.

Reading the result

The result line reads Cropped 12 page(s), with the file size beside it. The number should match the scope you chose: all pages in the document, or one. Open the downloaded file and page through it. A tight crop that looked fine on page 1 can cut a table or a signature that sits closer to the edge on page 9.

The size shown is close to the original. If a portal rejects the file for being too large, cropping will not help, and the right move is to reduce the file size afterwards.

When trimming margins helps

• Scans with dark borders where the scanner lid did not sit flat.
• Photographs of documents taken on a desk, once they have been turned into a PDF with the scan to PDF tool.
• Pages saved from a web page, with a URL and date running along the top or bottom.
• Certificates, mark sheets and receipts that have to fit a form or a template with a fixed frame.
• Slide handouts and diagrams that you want to paste without wide empty margins.
• Book scans where one side has a wide gutter.

Tips for a clean crop

• Page through the whole document before choosing Every page. The box you draw on page 1 is applied as the same fractions to every other page.
• Leave a little breathing room. Cutting exactly at the edge of the text makes a printed page look cramped and risks clipping a descender or a stamp.
• Choose This page only when a single page is different, such as a landscape table in a portrait report. Apply the crop again for other pages.
• If a scan was saved sideways, rotate the pages first so the box you draw matches what you see.
• Do the cropping before you add other marks. Page numbers placed first can end up outside the new visible area.

Mistakes to avoid

• Cropping to hide private details. The hidden area is still in the file and can be recovered. Use the redaction tool when something has to disappear for good.
• Cropping a file and expecting it to become smaller. Only compression changes size.
• Using Every page on a document whose pages are different sizes without checking a few of them.
• Cropping a file that was already cropped. The box is worked out against the page's full original area, so a second pass may not match what the preview shows. Keep the original and crop from that.
• Assuming every program honours the crop. Software that ignores the crop box shows the full original page.

Limits

The tool takes a single PDF of up to 100 MB and 500 pages, and it stops with a clear message for an empty file, a damaged file, or a PDF that is not really a PDF. A password-protected file is refused with a prompt to unlock it first; if you know the password, unlock the file and come back. It cannot crop each page to a different box in one pass. The box must be at least 5 per cent of the page in each direction, and you cannot crop to a named paper size.

Cropping runs in your browser, on your device. The PDF is not uploaded to a Jobsixo server, and no account or watermark is involved.