How to Generate PDF Alt Text Automatically: 4 Methods from Manual to AI-Powered (2025 Guide)

Missing alternate description – Figure or Formula Alt, Actual Text, Table Summary, Annotation Contents – is blocking millions of screen reader users from accessing your PDFs. Every image, chart, formula, and table needs a meaningful alt text for PDF/UA and WCAG compliance – but writing them manually is slow, expensive, 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.

Table of Contents hide

1. Method: Manual Tagging

Example 1.1: Set “Alt” key for <Figure> tags (manual_alt.pdf)

Example 1.2: Set “Contents” key for annotations (manual_annots)

2. Method: Auto-Tagging with a Pre-Defined Template

Example 2.1: Set “Alt” key for <Figure> tags ( layout_template_actual.zip)

3. Method: PDFix Basic Actions

Example 3.1: Set “Alt” key for <Figure> tags (basic_alt.pdf)

Example 3.2: Set “Contents” key for annotations (basic_annots.pdf)

Example 3.3: Set “Alt” key for <Link> tags (basic_annots.pdf)

Example 3.4: Set “ActualText” key for <Figure> tags (basic_actual.zip)

4. Method: External AI Actions

Example 4.1: Set “Alt” key for <Figure> tags (manual_alt.pdf)

Example 4.2: Set MathML associated files for <Formula> tags (external_mathml.pdf)

Batch Alternate Descriptions – Enterprise Automation

Scale Accessibility Across Hundreds of PDFs

How It Works

Review and Refinement: The Human Quality Pass

Summary – Choose the Right Alt Text Method for Your Workflow With PDFix

Next Steps

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1. Method: 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

Example 1.1: Set “Alt” key for <Figure> tags (manual_alt.pdf)

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.

2. Method: Auto-Tagging with a 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 other 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

Example 2.1: Set “Alt” key for <Figure> tags ( layout_template_actual.zip)

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

3. Method: PDFix 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 (Contents key)
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_update JSON 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.

Example 3.1: Set “Alt” key for <Figure> tags (basic_alt.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 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

You can also run this action automatically on the entire document from the main ribbon:
Annotations → Set Annotation Contents

Example 3.3: Set “Alt” key for <Link> tags (basic_annots.pdf)

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....

Example 3.4: Set “ActualText” key for <Figure> tags (basic_actual.zip)

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
  - Load basic_actual_green.json
- 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
  - Load basic_actual_red.json
- 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.

4. Method: 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.

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

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

Example 4.1: Set “Alt” key for <Figure> tags (manual_alt.pdf)

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.

Example 4.2: Set MathML associated files for <Formula> tags (external_mathml.pdf)

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)

Batch Alternate Descriptions – Enterprise Automation

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

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.

Summary – Choose the Right Alt Text Method for Your Workflow With PDFix

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.