Crop PDF

Crop PDF trims the margins of PDF pages: you draw or type the area to keep, and the saved file shows only that area on every page you choose. It is for cutting wide white borders off scanned pages, removing printer marks, focusing a slide or a figure for a presentation, or making a document easier to read on a phone or e-reader. The file is processed in your browser and never uploaded.

Choose a file and the first page appears with a crop box over it. Drag the box's edges or corners, drag inside it to move it, or draw a new box on the page; the four margin fields — Top, Right, Bottom and Left, in millimetres or points — update as you drag, and you can type exact values instead. Use the arrows to preview other pages. Each margin is measured from that edge of the page as you see it, and the same margins are applied to every page you choose, each from its own edges, so a document mixing A4 and Letter pages is trimmed evenly. Apply to all pages, or type a list such as 1-3, 5.

Cropping sets each page's CropBox — the rectangle PDF viewers display and print. The page's full size (its MediaBox) is left unchanged, so nothing is deleted: the content outside the box is still in the file, hidden rather than removed, and any PDF editor can reset the CropBox to bring it back. That makes cropping safe to undo, but it also means cropping is not a way to remove confidential information — anyone who receives the file can reveal what you trimmed. Text stays selectable and images are not recompressed, because the page content is not touched.

The maths handles awkward pages correctly: a page stored with a rotation (where the edge you see at the top is really the page's left edge in PDF coordinates), a page whose coordinate system does not start at zero, and a page that was already cropped, which is trimmed further from what you currently see. A crop must leave at least 10 points (about 3.5 mm) of width and height on every chosen page; if margins would leave less on any page, nothing is saved and the message names the page. One millimetre is 72 ÷ 25.4 ≈ 2.835 points.

Because the file is edited in place, bookmarks, links, form fields and metadata are kept; a digital signature stops validating, as with any edit. Password-protected and permission-locked PDFs are refused, and files up to 200 MB are accepted. Pages are previewed with pdf.js and saved with pdf-lib, both in your browser — you can check in the Network tab of your browser's developer tools that no request carries your PDF.

1. The file's first bytes are checked for the PDF signature, then pdf-lib opens it; encrypted and damaged files are refused. For each page the visible area (CropBox clipped to MediaBox, including inherited values) and the rotation are read. 2. pdf.js renders the previewed page; the crop box you drag is converted from screen pixels to points: margin = pixels × page width in points ÷ preview width in pixels. 3. Typed millimetres are converted with points = mm × 72 ÷ 25.4. 4. For each chosen page, the four displayed-edge margins are mapped to PDF coordinates according to its rotation (at 90° the displayed top is the page's left edge, the displayed right its top, and so on) and subtracted from its visible area. 5. Every page is checked first; if any would be left narrower or shorter than 10 points, nothing is changed and the page is named. 6. Each page's /CropBox is set to the new rectangle, the MediaBox is left alone, and the file is saved as <name>-cropped.pdf.