Lucia Todova
Co-Founder | Chief Architect of PDFix Technology & Automation
Quick Overview: You can generate PDF alt text automatically using AI-powered actions in PDFix Desktop or SDK – tools like Set Alternate Description (OpenAI or BLIP) read figures, tables, and formulas and write accessible descriptions in seconds. For full PDF/UA and WCAG compliance, pair automated generation with a short human review pass, or use manual tagging and layout templates for smaller or highly standardized documents.
Every image, chart, formula, and table needs a meaningful alt text for PDF/UA and WCAG compliance – but writing them manually is slow and doesn’t scale. This guide reveals 4 proven methods to automate PDF image alt text generation, from template-based workflows to advanced AI models that understand visual context.
❶ How Do You Add Alt Text to a PDF Manually?
MANUAL TAGGING
When to Use:
Best for unique, context-specific descriptions where accuracy matters more than speed.
How It Works:
The remediator selects each tag (Figure, Formula, Table, Annotation) and manually types the Alt, ActualText, Summary, or Contents.
PROS:
✓ Most accurate for unique or context-specific descriptions
CONS:
✕ Slow and repetitive
✕ Not scalable for larger document sets
Steps:
- Open PDF and validate the PDF in the Validation panel
- Navigate through the validation errors and manually update the Alternate Description in the Tag properties in the Tag panel
You can also navigate through the <Figure> tags directly in the Tag panel, or use the Search field and type “Figure” to filter and jump through figure elements only.
▣ Example 1.2: Set “Contents” key for annotations (manual_annots)
Steps:
- Open PDF and validate the PDF in the Validation panel
- Navigate through the
<Link>errors and manually update the Content field in the Annotation Properties in teh Annotation panel
You can also review annotations directly in the Annotation panel. Select an annotation and update its description in the Contents text edit in the Annotation Properties.
❷ How Does Auto-Tagging with a Template Generate Alt Text?
PRE-DEFINED TEMPLATE
When to Use:
Ideal for repetitive documents with consistent layouts – forms, reports, standardized publications. Learn more about Layout Templates in our detailed guide: 👉 https://pdfix.net/pdfix-desktop-auto-tagging/#auto-tagging-with-ai-template or explore additional insights in our webinars.
How It Works:
The Layout Template assigns predefined Alt or ActualText to detected objects automatically based on template rules.
PROS:
✓ Fast and consistent across repetitive documents
✓ Perfect for batch processing standardized files
CONS:
✕ Static descriptions — all matched objects get the same alt text
✕ Requires well-defined detection rules
Steps:
- Open the PDF and load layout_template_actual.json in the Template panel
- Set the “alt” value on the figure initial element
- Run AutoTag and review the generated Alternate Descriptions for all Figure elements
❸ What Are PDFix Basic Actions for Setting Alt Text?
BASIC ACTIONS
When to use:
Best for semi-automated workflows where you can reuse nearby text, captions, or existing content. This action lets you quickly set or update alt text for Figures, Formulas, Tables, or Annotations using regex filters or template-based rules.
What you can automate:
PDFix provides several targeted accessibility actions:
- Set Alternate Description – for images and formulas (Figure, Formula).
- Set Table Summary – for table tags
- Set Annotation Contents – for annotations (
Contentskey) - Set Actual Text – for any tag where text normalization or replacement is needed
How it works
- Select target tags using a regex or a
tag_updateJSON filter - Choose the source of the alt text: custom text, description tag above/below, child tags, or the tag’s own content
- Optionally overwrite existing alt text
PROS:
✓ Semi-automatic and flexible
✓ Reuses captions or nearby text.
CONS:
✕ Depends on correct tagging and document structure.
✕ Rules copy text but don’t interpret meaning
Steps:
- Open the PDF and validate it in the Validation panel
- Select the errors you want to fix and click Fix
- In the Set Alternate Description dialog:
- Alternate Description: Use the associated tag content….
You can also run this action automatically on the entire document from the main ribbon:
Tags → Set Alternate Description
▣ Example 3.2: Set “Contents” key for annotations (basic_annots.pdf)
Steps:
- Open the PDF and validate it in the Validation panel
- Select the errors you want to fix and click Fix
- In the Set Annotation Contents dialog:
- Select Annotations:
^(?!.Widget|.Popup).*$ - Contents: Text from annotation bounding box
- Select Annotations:
You can also run this action automatically on the entire document from the main ribbon:
Annotations → Set Annotation Contents
Steps:
- Open the PDF
- Run Tags → Set Alternate Description on the entire document from the main ribbon
- In the Set Alternate Description dialog:
- Tags:
Link - Alternate Description: Use the associated tag content....
- Tags:
Steps:
- Open the PDF
- Run Tags → Set Alternate Description on the entire document from the main ribbon
- In the Set Alternate Description dialog:
- Tags → Edit Values
- Alternate Description: Define the Custom Alternative text
- Custom Alternate: YES
- Run Tags → Set Alternate Description on the entire document from the main ribbon
- In the Set Alternate Description dialog:
- Tags → Edit Values
- Alternate Description: Define the Custom Alternative text
- Custom Alternate: NO
If you work with similar documents regularly, you can even create a Custom Action that combines both steps into a single automated workflow, allowing you to process the entire document much faster.
❹ How Do You Use AI to Automatically Generate Alt Text, Summaries, and Metadata?
EXTERNAL AI ACTIONS
When to use:
For scalable, intelligent alt text generation across diverse document types – especially images, complex tables, and mathematical formulas.
Available AI Models:
PDFix integrates multiple specialized AI engines via the Actions Marketplace. New models are added continuously as AI technology evolves.
PROS:
✓ Removes most manual writing of alt text and summaries
✓ Scalable for large batches and repetitive documents
✓ High accuracy for images, formulas, and tables
CONS:
✕ Requires correct tagging or detection
✕ Quality depends on PDF clarity and structure
✕ Cloud-based models require network access
✕ May produce overly detailed or too generic descriptions without guidance
CURRENT AI ACTIONS
- Generate Alternate Text (Salesforce BLIP) – Fast, stable model for generating basic image descriptions in bulk
- Generate Alternate Text (OpenAI) – Advanced multimodal model that understands images, charts, tables, and formulas with strong contextual accuracy
- Generate Formula MathML (OpenAI) – Converts formulas into accessible MathML with high precision
- Generate Formula MathML (Paddle) – Robust alternative engine suitable for scientific documents and weaker-quality PDFs
- Generate Table Summary (OpenAI) – Creates screen-reader-friendly summaries of complex tables
Steps:
- In the Tag panel, select the Figure tags for which you want to generate alternate text
- Click Run Action on Selection → Set Alternate Description (OpenAI)
- In the Set Alternate Description dialog:
- OpenAI API Key: Enter your OpenAI credentials
- Model: Select the AI model you want to use
- Prompt: Adjust the prompt for image description if needed
- Language: Choose the desired language for the generated alternate description
The same action can also be used to generate Alternate Descriptions for Formula tags.
Steps:
- In the Tag panel, select the Formula tags for which you want to generate MathML assocciated file
- Click Run Action on Selection → Set Formula MathML (Paddle)
❺ How Do You Batch-Generate Alt Text Across Hundreds of PDFs?
Scale Accessibility Across Hundreds of PDFs
All actions – Basic PDFix Actions and External AI Actions – can be executed in Application View inside PDFix Desktop as a fully automated batch process. This allows you to apply Alt text, MathML, table summaries, tagging rules, or any other operation across hundreds of PDFs with a single workflow.
How It Works
PDFix Desktop:
- Build a processing pipeline directly in Application View
- Combine multiple actions (tagging + AI alt text + validation)
- Reorder actions to optimize workflow
- Run on entire folders of documents
PDFix SDK:
- The same actions and workflows available programmatically
- Full automation in server environments
- Custom integrations with existing document management systems
- Headless processing for enterprise-scale remediation.
Pros:
- ✅ Fully automated workflows for large batches
- ✅ Same interface and logic in Desktop UI and SDK
- ✅ Combine multiple actions into single pipeline
- ✅ Enterprise-ready for server deployment
Cons:
- ❌ Requires initial setup of action order and configuration
- ❌ Performance depends on document complexity and hardware
◆ Do AI-Generated Alt Text Descriptions Still Need Human Review?
Even with templates, basic actions, and AI assistance, alternate descriptions still benefit from a final human pass. To ensure true accessibility:
- Review AI-generated alt text, MathML, and table summaries for accuracy and intent
- Check that Figures, Formulas, Tables, and Annotations received the correct type of description
- Verify that decorative images remain correctly marked and that meaningful visuals are described
- Run the accessibility checker and resolve remaining logical or structural issues
Alternate descriptions are critical for users with visual impairments — and small manual refinements can significantly improve clarity and usability.
◆ Which Method Should You Use to Generate PDF Alt Text?
With PDFix Desktop and SDK, you have multiple ways to generate and refine alternate descriptions:
- Manual tagging for the highest control in complex or unique cases
- Layout Templates for consistent, predefined alt text in repetitive documents
- Basic PDFix Actions for semi-automatic updates based on regex or template filters
- AI Actions (Alt Text, MathML, Table Summary) for fast, scalable, and intelligent generation
- Batch processing in Application View, or full automation through the SDK
The best remediation strategy combines multiple methods: Use templates for standardized content, AI for visual interpretation, and human review for quality assurance
By combining these approaches, PDFix helps you produce accurate, scalable, and fully accessible alternate descriptions across all your PDFs -meeting PDF/UA and WCAG compliance without the manual bottleneck.
Next Steps
- Download PDFix Desktop and try automated alt text generation
- Explore the Actions Marketplace for the latest AI models
- Learn more about PDFix SDK for enterprise automation
- Watch the PDFix Webinar
Frequently Asked Questions
How do I use AI to automatically generate alt text, summaries, and metadata for a PDF?
In PDFix Desktop, select the Figure, Table, or Formula tags in the Tag panel, then run the matching AI action – Set Alternate Description for images, Generate Table Summary for tables, or Generate Formula MathML for equations. Each action connects to a chosen AI model (OpenAI or BLIP) and writes the result directly into the tag. The same actions are available programmatically through PDFix SDK for batch processing.
What does “annotation has alt text” mean in a PDF/UA validation report?
It means the validator found a Link or other annotation missing a Contents entry, which PDF/UA and WCAG require so screen readers can announce the annotation’s purpose. Fix it with the Set Annotation Contents action, or manually add the Contents key in the Annotation Properties panel.
What does “figure has alt text” mean in a PDF/UA validation error?
It flags a <Figure> tag with no Alt entry. You can resolve it through manual tagging, a layout template with predefined Alt values, or an AI action such as Set Alternate Description (OpenAI/BLIP).
Is there a PDF alt text API?
Yes. PDFix SDK exposes the same alt text, table summary, and MathML actions available in PDFix Desktop programmatically, so you can generate and apply alternate descriptions across hundreds of PDFs in a server or pipeline environment.
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PDF Accessibility Checker
Free PDF accessibility validator. Instantly check compliance for WCAG 2.2, PDF/UA, and Section 508. Fast, cross-platform tool for document audits.
PDF Remediation Tool
AI-powered PDF accessibility remediation tool. Auto-tag complex PDFs, tables and automate PDF/UA fixes for high-volume workflows.
PDF Accessibility API
Enterprise PDF accessibility SDK for integrating automated tagging, remediation, and validation into scalable document workflows across US and EU compliance requirements.
