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How to make PDFs accessible

Colour contrast

Colour contrast is the difference between two colours. Colours with good contrast stand out from each other. Colours with poor contrast look similar and can be difficult to tell apart.

Factors like tiredness, screen displays, light levels, age and visual impairments can all affect how difficult it is to tell colours with poor contrast apart.

Using good colour contrast means more people can understand and navigate your PDF.

Go to YouTube to watch a video on the importance of colour contrast.

What to check

Colour contrast ratio measures the difference between two colours using numbers. You should use colour contrast ratio to check that colour combinations in certain parts of your PDF have accessible contrast.

Text

Normal text is unbolded text under 18 point/24px and bolded text under 14 point/18.5px. Normal text colour and the colour behind it must have a colour contrast ratio of at least 4.5:1.

Large text is unbolded text that is 18 point/24px and above and bolded text that is 14 point/18.5px and above. Large text colour and the colour behind it must have a colour contrast ratio of at least 3:1.

Links

Links include linked text and images. Link colour and the colour behind it must have a colour contrast ratio of at least 3:1

Non-text content in informative images

Colours that are next to each other in informative images must have a colour contrast ratio of at least 3:1.

For example, if you had a pie chart in your PDF, you'd need to make sure that:

  • The pie chart's segment colours and the PDF's background colour have good colour contrast
  • The colours of segments next to each other have good colour contrast

Our images accessibility page has advice on how to decide if an image is informative or decorative.

Decorative images and logos do not have to have accessible colour contrast.

How to check colour contrast

WebAIM's Contrast Checker (opens new window) (opens in a new window) helps you check how accessible any colour combination is. To use this tool, you'll need to know the hex codes for your colours. A hex code is a hash (#) followed by 6 numbers that references a specific colour.

To get a colour's hex code, take a screenshot of the colour you're checking in the PDF. Then upload it to an online image colour picker, like the Image Color Picker tool (opens new window) (opens in a new window), to get the hex code.

How to correct colour contrast

If you find that any colour combinations you use don't have accessible contrast, you must fix them.

The easiest way to fix them is to edit your source document (eg Word), and then reconvert it to a PDF.

If you need to go back to your original Word document, read our guide on colour contrast in Word. You may find our Word accessibility advice useful even if you used a different application to create your PDF.

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