PDF Tools·3 min read

Converting a PDF to Grayscale Without Losing Text

The print shop charges three times more for colour pages, and your 40-page report has a coloured logo on every page. Or a government portal insists on black and white scans, and your phone photographed the form in full colour. Both problems need a grayscale PDF, but there are two very different ways to make one, and the wrong one can wreck your text. This guide explains how the Grayscale PDF tool's Keep text mode and Rasterize modes work, and when to use each.

Open the free Convert PDF to Grayscale All insights

Why people need grayscale PDFs

Cost, rules and predictability.

Printing is the most common reason. Many printers and print shops charge more for any page with colour on it, and a single blue link or coloured logo can turn a text page into a colour page. A gray PDF removes the surprise.

Rules are the second reason. Exam boards, courts and government portals often ask for black and white documents, and some check. Archiving is a third: grayscale scans are smaller and read just as well for text documents. Accessibility can be a fourth. Colour-coded charts become hard to read for some people once printed on an office laser printer, and checking the gray version first shows whether the chart still makes sense without colour.

How Keep text mode works

Change the colour, not the page.

A PDF page is a list of drawing instructions, and colours are set by short commands before text and shapes are drawn. Keep text mode rewrites those commands to the matching gray, using the usual brightness formula, so dark red becomes dark gray and pale yellow becomes light gray. The text itself is untouched, so it stays sharp, selectable and searchable.

Photos are decoded and saved again in gray, palette images get a gray palette, and simple gradients are made gray. The file size usually stays about the same, and links, bookmarks and form fields keep working because the page structure is not rebuilt. A few rarer items can stay in colour, such as CMYK JPEG photos, JPEG 2000 images and complex shadings, which is why the tool shows a preview of the result before you download.

When to rasterize instead

Every pixel gray, at a price.

Rasterize, grayscale draws each page as an image, turns it gray and builds a new PDF from those images. It catches everything, including the rare colours Keep text mode skips, but the text becomes part of a picture and can no longer be selected or searched.

Rasterize, black and white goes further and uses only pure black and pure white, like a photocopier. It suits scanned forms and signatures, where it removes paper tint and shadows, and it often makes scans much smaller. It is a poor choice for photos, which turn into rough dots. Pick 200 DPI for most documents and 300 DPI when fine print matters. Both raster modes rebuild every page, so links, bookmarks and form fields do not survive; keep the original if you need them.

A worked example: a report for the print shop

Keep text first, check, then decide.

Input: annual-report.pdf, 40 pages with a blue header, coloured charts and six photos. Drop it in, keep Keep text selected, and press Convert to grayscale. The file line reports how many content streams, images and gradient colours were converted, and the preview shows the result.

Scroll the preview. The header and charts are gray, the photos are gray, and the text is still text. If one chart built from a complex gradient still shows colour, convert again with Rasterize, grayscale at 300 DPI for print, and accept that the text is no longer selectable in that copy. Download annual-report-grayscale.pdf and send it to the printer.

Mistakes to avoid

Small choices, big differences.

These cause most disappointing results.

Rasterizing a text document by default. It loses selectable text and can make the file bigger. Start with Keep text.
Using black and white on photos. Photos need grayscale to keep their detail.
Skipping the preview. A quick scroll catches any element that stayed in colour.
Choosing 150 DPI for print. It looks fine on screen but soft on paper; use 300 DPI for printing.
Forgetting the printer settings. Some printers still mix coloured inks for gray unless you also choose grayscale in the print dialog.

Related tools

What pairs well with a gray PDF.

Compress PDF has its own Convert images to grayscale option, which grays only the photos while it shrinks them, handy when size matters more than the colour of the text. PDF to JPG and PDF to PNG can export grayscale or black and white page images directly.

For scans that are both colourful and heavy, run Grayscale PDF with Rasterize, black and white first, then Compress PDF if the file still needs to shrink. Everything runs in your browser, so the documents never leave your device.