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Accessible PDFs in .NET with PDF/UA

An accessible PDF is one that people who use screen readers, magnifiers or keyboards can read as well as anyone else. Visually it looks like any other PDF; what makes the difference is a structure tree inside it, which says what each thing on the page is (a heading, a paragraph, a table cell, an image and its description) and the order to read them in. That is a tagged PDF, and PDF/UA (ISO 14289) is the standard that says what a tagged PDF must contain to be accessible.

Accessibility is also a legal requirement more and more often: the European Accessibility Act applies to many digital services in the EU from June 2025, public bodies in the EU and the US (Section 508) have required it for longer, and customers increasingly ask for it. Check which rules apply to you.

Why it is hard in .NET, and what Tagua does

Section titled “Why it is hard in .NET, and what Tagua does”

Most PDF libraries draw text and lines at positions, and tagging is left to you: every paragraph, heading and table cell has to be wrapped in the right structure element, in reading order, by hand. Report writers mostly produce untagged PDFs. So accessible documents usually need a separate remediation step.

Tagua tags every document by default, from the template:

  • Text is a paragraph (P); tag: h1 to h6 makes it a heading. Headings must start at h1 and not skip levels.
  • Tables become real tables: header cells (TH) with their scope, rows and data cells, even across pages.
  • Images and barcodes are figures with the alternative text you give in alt.
  • Page headers and footers, and anything you mark tag: artifact, are kept out of the reading order.
  • Links are tagged as links, with their target described for assistive technology, and the document has a title and a language.

With compliance: [pdf-ua-1], Tagua checks the template for what PDF/UA requires before any data is read: a title, a language, alternative text for every image, embedded fonts and headings in order. A mistake is an error with its location, not a document that fails later.

An example

Section titled “An example”

This report is PDF/UA-1. It passes veraPDF, the reference validator, and you can download the PDF to try it with a screen reader.

accessible-report.report.yaml
# An accessible report (PDF/UA-1): a title and a language, headings in order, a table with header cells, alternative
# text for the image, a decorative rule kept out of the reading order, and a link.
title: Accessibility review, third quarter
language: en-GB
culture: en-GB


document:
  author: Contoso Ltd
  compliance: [pdf-ua-1]


fonts:
  Inter: { regular: fonts/Inter-Regular.ttf, bold: fonts/Inter-Bold.ttf }


styles:
  default: { font: Inter, fontSize: 10pt, lineHeight: 1.4 }
  th: { fontWeight: bold, borderBottom: "0.75pt solid #3E2A1A", padding: 0 0 3pt 0 }


data:
  services: { fields: { Service: string, Documents: int32, Passed: int32 } }


body:
  reportHeader:
    - gap: 8pt
      content:
        - { type: image, source: banner.png, width: 180pt, alt: "Tagua: accessible, archival PDF reports for .NET" }
        - { type: text, value: "Accessibility review, third quarter", fontSize: 18pt, fontWeight: bold, tag: h1 }
        - type: text
          value: >-
            Every document our services produced this quarter was checked against PDF/UA. This table shows how many
            passed, by service.
        - { type: text, value: Results by service, fontSize: 13pt, fontWeight: bold, tag: h2 }
        - type: table
          dataset: services
          headerStyle: th
          columns:
            - { header: Service, value: "{Service}", width: 3fr }
            - { header: Documents, value: "{Documents:N0}", width: 1fr, align: end }
            - { header: Passed, value: "{Passed:N0}", width: 1fr, align: end }
            - { header: Rate, value: "{Passed / Documents:P0}", width: 1fr, align: end }
          footer:
            - cells:
                - { value: Total, isHeader: true, fontWeight: bold }
                - { value: "{Sum(Documents):N0}", align: end, fontWeight: bold }
                - { value: "{Sum(Passed):N0}", align: end, fontWeight: bold }
                - { value: "{Sum(Passed) / Sum(Documents):P0}", align: end, fontWeight: bold }
        - { type: line, stroke: "0.5pt solid #A3968A", tag: artifact }
        - type: text
          value: How the documents are checked is explained at taguareports.com.
          link: https://taguareports.com


  pageFooter:
    - content:
        - { type: text, value: "Page {PageNumber} of {TotalPages}", fontSize: 8pt, align: end }
accessible-report.data.yaml
data:
  services:
    - { Service: Invoicing, Documents: 18240, Passed: 18240 }
    - { Service: Statements, Documents: 9120, Passed: 9054 }
    - { Service: Letters, Documents: 2305, Passed: 2251 }
The rendered report: the Tagua banner, a heading, a paragraph, a table of documents checked and passed per service with a total row, and a link.

What makes it accessible:

  • title and language (en-GB): the title is shown in the viewer’s title bar and read first; the language tells a screen reader how to pronounce the text. An element in another language takes its own language.
  • tag: h1 and tag: h2 give the document an outline that screen readers navigate by.
  • The table’s header row becomes TH cells, and isHeader: true makes the footer’s “Total” a row header, so each number is read with its column and row.
  • alt describes the image. A decorative image would be tag: artifact instead.
  • The rule under the table is tag: artifact: it is decoration, not content.
  • The fonts are embedded (fonts), so the text can be extracted exactly, which PDF/UA requires.

Render it from C# like any other report (see your first report), or with tagua render accessible-report.report.yaml.

PDF/UA-1 or PDF/UA-2

Section titled “PDF/UA-1 or PDF/UA-2”

pdf-ua-1 (2014) is what most checkers and procurement requirements ask for today. pdf-ua-2 (2024) is based on PDF 2.0; Tagua writes a PDF 2.0 file for it, and it combines with pdf-a-4 or pdf-a-4f rather than PDF/A-2 or PDF/A-3. Accessibility and archiving combine well: compliance: [pdf-a-2b, pdf-ua-1] gives a document that is both. See PDF/A in .NET.

Checking the result

Section titled “Checking the result”

  1. Validate it with veraPDF, which checks the machine-checkable rules of PDF/UA:

    Terminal window
    verapdf -f ua1 accessible-report.pdf

    Tagua’s own tests run veraPDF on every sample on every change.

  2. Check it with PAC, the free PDF Accessibility Checker, which also shows the structure tree and a screen reader preview.

  3. Listen to it with a screen reader: NVDA on Windows, VoiceOver on macOS. Validators check the rules; only a person can tell whether the alternative text is useful and the reading order makes sense.

Next

Section titled “Next”