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PDF/A & accessibility

Beyond a basic PDF lie two goals — PDF/A (a long-term archival standard, fully self-contained, required by many repositories and journals) and accessible, tagged PDF (readable by screen readers; the standard is PDF/UA). LaTeX reaches both through the pdfx package and the tagpdf / \DocumentMetadata machinery.

PDF/A — the archival standard

PDF/A is an ISO standard for long-term archiving that requires everything to be self-contained — fully embedded fonts, no encryption, XMP metadata, and a color output intent (ICC profile). Repositories, libraries, and thesis submissions often require it. The pdfx package produces it: \usepackage[a-2b]{pdfx} (also a-1b, a-3b). It reads metadata from a \jobname.xmpdata file and embeds an ICC profile (sRGB by default).

latex
% document.tex
\documentclass{article}
\usepackage[a-2b]{pdfx}   % document.xmpdata を読む / reads document.xmpdata

% document.xmpdata（別ファイル）
\Title{論文のタイトル}
\Author{山田 太郎}
\Keywords{LaTeX\sep PDF/A}

Conformance levels: PDF/A-1b (basic, PDF 1.4-based), PDF/A-2b (PDF 1.7 features such as transparency), and -3b (allows attachments). The trailing “b” is basic (visual) conformance, while the “a” levels additionally require tagging (accessibility). The print-oriented sibling standard is PDF/X.

Accessible PDF — tagging and PDF/UA

A tagged PDF embeds the logical structure — headings, paragraphs, lists, reading order, alt text — so a screen reader can navigate it. The accessibility standard is PDF/UA (UA-2 was published in 2024). The LaTeX team’s tagpdf package (by Ulrike Fischer) provides the tagging tools (low-level commands like \tagstructbegin) for pdfLaTeX/LuaTeX.

The modern entry point — \DocumentMetadata

Recent LaTeX (2025-06 onward) centralizes all of this. Put \DocumentMetadata{...} *before* \documentclass and it loads the PDF management layer, letting you request automatic tagging (tagging=on) and PDF/A output from one place. The LaTeX Project’s tagging initiative is moving toward automatically generating PDF/UA-2 / WTPDF-compliant accessible PDF, including auto-embedding MathML for math. This is the entry point to use going forward (the interface is still evolving — check the current docs).

latex
% \documentclass より前に / before \documentclass
\DocumentMetadata{
  lang=ja,
  pdfstandard=A-2b,
  tagging=on
}
\documentclass{article}

Practical notes

  • If the destination requires PDF/A → pdfx (a-1b/a-2b) plus title/author in \jobname.xmpdata.
  • Fonts must be fully embedded (pdflatex/lualatex embed by default — but verify).
  • For accessibility (PDF/UA) → \DocumentMetadata + tagpdf (automatic tagging is maturing).
  • Validate conformance with a tool like veraPDF (checks PDF/A and PDF/UA).

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