Lucia Todova
Co-Founder | Chief Architect of PDFix Technology & Automation
Quick Overview: The Set Annotation Contents action in PDFix Desktop adds or fixes the descriptive text screen readers use for annotations — the Contents key for links, highlights, and comments, or the TU key for form field widgets. It fixes common PDF/UA and WCAG validation failures like missing, empty, or whitespace-only annotation descriptions, either by pulling text from the annotation’s bounding box or destination, or by setting custom text for decorative elements.
Creating an accessible PDF isn’t just about tagging text — it’s also about making sure every annotation, from highlights to form fields, has meaningful, screen-reader-friendly descriptions. With PDFix Desktop’s Set Annotation Contents feature, you can easily add or update alternative text for annotations, ensuring that blind and visually impaired users receive the same contextual information as sighted readers — while keeping your documents compliant with industry accessibility standards.
What Does the “Set Annotation Contents” Action Do?
The Set Annotation Contents action in PDFix Desktop lets you define or update the descriptive text associated with a PDF annotation’s Contents key (for most annotation types) or TU key (for form field widgets). This text is what assistive technologies like screen readers use to describe an annotation’s purpose or function.
By using this feature, you can:
- Add custom alternative text (e.g., “Go to Page 3”, “Decorative”, “Click to Submit”)
- Extract visible text inside a highlight or annotation bounding box
- Describe interactive elements such as links, form fields, and buttons
- Automatically generate content based on document context or annotation actions (e.g., URI or page destinations)
By ensuring annotations are described accurately, you close accessibility gaps, improve navigation for assistive technology users, and meet key compliance requirements without tedious manual editing.
Best Practice Recommendations
- Review all configurable parameters to understand which ones can be adjusted for your use case
- Use
"Text from annotation bounding box"when the annotation visually highlights clear text (e.g.,Link,Underline,Highlight) - Use
"Action destination"forLinkannotations to describe where the link leads (e.g. “Go to Page 4” or “Open external URL”) Widget(form field) – SetTUkey using custom or layout-based content- Use
"Custom text"(e.g."Decorative") to mark visual annotations that are non-semantic - Always enable the Overwrite when cleaning old or non-compliant annotations
How PDFix Stands Out
Compared to traditional tools, PDFix Desktop allows precise and repeatable annotation tagging.
- Integrated with visual layout analysis for smart content extraction
- Supports batch tagging and template-based workflows
- Editable JSON configurations for automated accessibility pipelines
- Complies with latest accessibility standards (PDF/UA, WCAG)
Frequently Asked Questions
What does “annotation has alt text” mean for PDF/UA compliance?
It means a validator checked whether a PDF annotation (link, highlight, comment, etc.) has a Contents entry that assistive technology can read. If it’s missing, empty, or generic, the annotation fails PDF/UA and WCAG checks — fix it by setting real descriptive text via the Set Annotation Contents action.
What does “form field has TU key” mean in PDF/UA?
Form field widgets use a TU (tool tip / user name) key instead of a Contents key for their accessible description — e.g., “Enter your email address” for a text field, or “Click to Submit” for a button. PDFix Desktop sets this automatically from custom text or layout-based content.
What does “Contents entry on an annotation exists but is only composed of whitespace” mean?
The annotation technically has a Contents key, but it contains only spaces or blank characters — which validators treat the same as missing alt text, since a screen reader has nothing meaningful to announce. Fix it by re-running Set Annotation Contents with Overwrite enabled so the blank value gets replaced with real text.
How do I add alt text to a PDF link or highlight automatically?
Use the Set Annotation Contents action’s “Text from annotation bounding box” option to pull the visible text for highlights and underlines, or “Action destination” for links, which describes where the link goes (e.g., “Go to Page 4” or “Open external URL”).
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