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OS Authority

Convert a colour PDF to grayscale

Colour printing costs more, and some offices and exam portals ask for black-and-white documents. This tool turns every page of a PDF grey, including photos, charts and coloured text, and keeps the page sizes as they were.

Your PDF is processed on this device and never uploaded. We don't see, store or log your files.

How it works

  1. Tap Choose file and pick your PDF.
  2. Choose Standard (150 DPI) or Print (300 DPI).
  3. Tap Convert to grayscale.
  4. Download or share the grey PDF.

Why convert here

Your PDF never leaves your device. Every colour on the page is converted, not just the images, so nothing is left in colour by mistake. Free, with no watermark and no sign-up.

How it works and what changes

Each page is drawn by your browser, turned grey and saved as an image page of exactly the same size. At 150 DPI an A4 page becomes 1240 × 1754 pixels, sharp on screen and fine for most printing; at 300 DPI it is 2480 × 3508 pixels, for small print and photos, with a file roughly three to four times larger. Because pages become images, text can no longer be selected or searched, and links stop working. Keep your original if you need those.

Grayscale or pure black and white?

Grayscale keeps shades of grey, so photos and shaded charts stay readable. It is what printers and most portals mean by black and white. Pure black and white (only black or white dots) suits clean text but turns photos into blotches, so this tool does not offer it.

Frequently asked questions

Will the PDF get smaller?

Often for colour scans and photo-heavy files. A text document made in Word may get larger, because its text becomes an image. Use Compress PDF afterwards if size matters.

Can I still copy text from the result?

No. The pages become images. Copy the text from your original first, for example with PDF to Text.

Does it change the page size or layout?

No. Every page keeps its size and orientation.

Is my PDF uploaded?

No. Everything happens in your browser on your own device.

Last reviewed: October 1, 2026

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