Alternative Text in PDFs

What is alternative text?

Alternative text (alt text) is a text description of images, graphics, charts, and other visual elements in a PDF document. This text is read by screen readers and other assistive technologies to convey the meaning and purpose of visual content to users who cannot see it.

In PDFs, alternative text serves the same purpose as alt attributes in HTML - it provides a text alternative that describes the essential information conveyed by images, diagrams, charts, and other visual elements.

When to add alternative text

Alternative text should be provided for:

  • Informative images: Photos, illustrations, or graphics that convey important information
  • Functional images: Images that serve as buttons, links, or other interactive elements
  • Charts and diagrams: Visual representations of data or processes
  • Complex images: Images that require detailed description of their content
  • Images of text: When text appears within an image

Decorative images that don't convey meaningful information should be marked as artifacts rather than given alternative text.

Writing effective alternative text

Good alternative text follows these principles:

Be concise but complete

  • Describe the essential information the image conveys
  • Keep descriptions brief while including necessary details
  • Aim for one to two sentences for most images

Consider context

  • Relate the description to the surrounding content
  • Don't repeat information already provided in nearby text
  • Focus on why the image is included in the document

Describe function, not appearance

  • Explain what the image does or represents, not just what it looks like
  • For charts, describe the data trends, not just the visual appearance
  • For functional images, describe the action or destination

Use clear language

  • Write in plain language that matches the document's tone
  • Avoid phrases like "image of" or "picture showing"
  • Be objective and factual in descriptions

Adding alternative text in PDFs

Alternative text can be added to PDFs using several methods:

In source applications

  • Microsoft Word: Add alt text to images before converting to PDF
  • PowerPoint: Use the Format Picture > Alt Text feature
  • InDesign: Add alt text in the Object Export Options

In Adobe Acrobat

  1. Right-click on an image and select "Edit Alternate Text"
  2. Enter descriptive text in the dialog box
  3. Click OK to save the alternative text

Using the Tags panel

  1. Open the Tags panel in Adobe Acrobat
  2. Find the Figure tag containing the image
  3. Right-click and select Properties
  4. Add alternative text in the Alternate Text field

Best practice: Add alternative text in source applications when possible, as this preserves the text through the PDF creation process.

Marking decorative images

Decorative images that don't convey meaningful information should be marked as artifacts so they're ignored by assistive technologies:

What are decorative images?

  • Purely decorative graphics or designs
  • Background images or patterns
  • Spacer images or dividers
  • Images used only for visual appeal

Marking as artifacts in Acrobat

  1. Open the Content panel
  2. Right-click on the decorative image
  3. Select "Create Artifact"
  4. Choose appropriate artifact type (decorative)

Using the Tags panel

  1. Find the Figure tag for the decorative image
  2. Right-click and select "Change Tag to Artifact"
  3. The image will be removed from the tag structure

Properly marking decorative images prevents screen readers from announcing them, reducing unnecessary interruptions for users.

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