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How to Automate PDF Accessibility: Auto-Tagging Untagged PDFs with OpenDataLoader

Cowrie
Cowrie
Dev @ Bswen

Problem

PDF accessibility regulations are now enforced worldwide. The European Accessibility Act deadline was June 28, 2025. ADA and Section 508 are already in effect. Millions of existing PDFs lack structure tags, making them invisible to screen readers. Manual remediation costs $50—$200 per document and doesn’t scale.

The OpenDataLoader Approach

Built in collaboration with the PDF Association and Dual Lab (veraPDF developers), OpenDataLoader uses its layout analysis engine to detect document structure and generate accessibility tags automatically. The output follows the PDF Association’s Well-Tagged PDF specification.

The Four-Step Pipeline

Step 1: Audit Existing Tags

Use use_struct_tree=True to read existing PDF tags and detect untagged documents.

Audit existing PDF tags
import opendataloader_pdf


opendataloader_pdf.convert(
    input_path=["existing.pdf"],
    output_dir="audit/",
    use_struct_tree=True
)

Step 2: Auto-Tag to Tagged PDF

Use format="tagged-pdf" to generate structure tags. This is free under Apache 2.0.

Auto-tag untagged PDF
opendataloader_pdf.convert(
    input_path=["untagged.pdf"],
    output_dir="output/",
    format="tagged-pdf"
)
CLI equivalent
opendataloader-pdf --format tagged-pdf untagged.pdf -o output/

Step 3: Export PDF/UA (Enterprise)

Convert to PDF/UA-1 or PDF/UA-2 compliant files — enterprise add-on.

Step 4: Visual Studio (Enterprise)

Review and fix tags with a graphical editor.

Combined Extraction and Tagging

Data + accessibility in one pass
opendataloader_pdf.convert(
    input_path=["document.pdf"],
    output_dir="output/",
    format="json,tagged-pdf"
)

Validation with veraPDF

Auto-tagging is validated using veraPDF, the industry-reference PDF/A and PDF/UA validator. This ensures standards-compliant output, not just heuristic tagging.

Summary

In this post, I showed how to automate PDF accessibility with OpenDataLoader. The key point is that the core auto-tagging pipeline is free under Apache 2.0, validated with veraPDF, and replaces manual remediation workflows costing $50—$200 per document.

Final Words + More Resources

My intention with this article was to help others share my knowledge and experience. If you want to contact me, you can contact by email: Email me

Here are also the most important links from this article along with some further resources that will help you in this scope:

Oh, and if you found these resources useful, don’t forget to support me by starring the repo on GitHub!

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