Crop PDF margins
Cropping a PDF sets each page's crop box — the rectangle viewers display and print — inward by the margins you specify, hiding white space and scanner borders. The trimmed content is hidden, not deleted, and everything runs locally in your browser with no upload. Typical uses: tightening oversized margins for e-reader screens, cutting off scanner edges, and framing a figure before embedding it elsewhere.
One thing to be clear about before you crop: this operation changes what is shown, not what is stored. If your reason for trimming an edge is that it contains names, stamps or account numbers, cropping is the wrong tool — use Redact PDF, which flattens the page so the removed content genuinely no longer exists in the file.
How it works: media box versus crop box
The PDF specification (ISO 32000) gives every page a set of nested boundary rectangles. The media box is the full physical page as created; the crop box, which defaults to the media box when absent, is the region “to which the contents of the page shall be clipped when displayed or printed.” Viewers — Acrobat, Preview, browsers — show the crop box as if it were the whole page: it defines the visible size, the zoom-to-fit behavior, and the print area.
This tool reads each page’s current dimensions, subtracts your top, bottom, left and right trim amounts (entered in millimeters and converted to points at 72 per inch), and writes the resulting rectangle as the page’s new crop box. The content streams, fonts and images are not modified at all; a page’s drawing instructions still describe the full original page, and the viewer simply stops displaying the strip you trimmed. That makes cropping instant, perfectly lossless and fully reversible — setting the crop box back to the media box restores the page exactly.
The same property is the caveat: nothing outside the crop box is removed from the file. Text in a hidden margin still turns up in search, text extraction and copy-paste, and any PDF editor can widen the box again. Cropping is presentation, redaction is removal — pick by whether the hidden content is merely unwanted or actually sensitive. Note also that some tools ignore the crop box in favor of the media box (a few printers’ drivers and image converters), which is worth a test print if exact output size matters.
Worked example: making a two-column paper readable on a 7-inch e-reader
An academic paper: 14 pages of A4 (210 × 297 mm), 1.9 MB, with generous 25 mm margins on every side. On a 7-inch e-reader the full A4 page renders text at roughly 6.5 pt equivalent — unreadable without constant panning. Cropping 22 mm from left and right and 20 mm from top and bottom leaves a 166 × 257 mm text block: the visible page area drops by about 32%, so the same screen now shows the text about 27% larger in each direction. The output file is 1.9 MB — unchanged, since only 14 crop-box rectangles were written — and the operation took well under a second. Page numbers sitting 12 mm from the bottom edge disappeared from view with the trim, which was acceptable here; they are still in the file and searchable.
Cropping PDFs — frequently asked questions
Does cropping a PDF permanently delete the trimmed content?
No. Cropping only changes which rectangle viewers display; everything outside it remains stored in the file and can be restored by resetting the crop box. To remove sensitive content irreversibly, use a redaction tool that flattens pages.
How do I remove the black edges from a scanned PDF?
Measure roughly how wide the dark border is, then crop that amount from each affected edge, for example 8 mm all round. The borders come from the scanner lid or page misalignment and sit at the extreme edges, so a uniform trim removes them cleanly.
Will cropping reduce my PDF file size?
No, or only trivially. The content outside the crop box stays in the file, so the data is all still there; only a few geometry values change. If size is the goal, compress the PDF instead.
Can I crop every page of a PDF by the same amount at once?
Yes. You enter one set of top, bottom, left and right margins and the tool applies it to every page in a single pass. Uniform trims suit e-readers well because consistent page geometry keeps the zoom level stable.
Why does my cropped PDF print with margins anyway?
Most printers have an unprintable border of about 4 to 6 mm, and print dialogs often re-add scaling to fit it. Choose actual size rather than fit-to-page in the print dialog, or accept the small hardware margin.
Is cropping a good way to hide confidential information at the page edge?
No. The hidden strip is still inside the file and trivially recoverable, and copy-paste or text extraction can still reach it. Redaction, which removes the underlying content, is the safe method.