Convert a PDF to grayscale — without uploading

Converting a colour PDF to grayscale is normally a printing decision — and the documents heading for a printer are often contracts, statements, or reports you would rather not route through a stranger's server on the way. The conversion runs here with Ghostscript compiled to WebAssembly, entirely in your browser. Nothing is transmitted; this site has no backend, and a Content-Security-Policy blocks third-party requests.

• Predictable printing. Left to itself, a printer converts colour to grey using its own logic, and the results are frequently muddy — light blues vanish, reds and greens collapse to the same flat tone, coloured text loses contrast against the page. Converting first means you see exactly what will print.
• Smaller files. Grey pixels carry roughly a third of the data of colour ones, so image-heavy and scanned documents often shrink noticeably.
• A uniform look. A bundle assembled from several sources — some scanned in colour, some in black and white, some exported from different applications — reads as one document rather than a patchwork.
• Cost and toner. Some print shops and office printers charge per colour page regardless of how little colour a page actually uses.

Only colour is converted. Text stays text and vector graphics stay vectors, so everything remains sharp at any zoom and text remains selectable and searchable in the output. Pages are not rasterised into pictures — a shortcut some converters take that quietly destroys both searchability and print quality.

You see the before and after sizes when it finishes, so the saving is a measured result rather than a claim. Do check the output if the original used colour to carry meaning: a chart whose series are distinguished only by colour, or a form with red required-field markers, can lose that distinction once everything becomes a shade of grey.

If the goal was primarily a smaller file, Compress PDF usually achieves more, and the two combine well — grayscale first, then compress, both on your device.