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About the contributor
Duff Johnson

A veteran of the electronic document space, Duff Johnson is an independent consultant, Executive Director of the PDF Association and ISO Project co-Leader (and US TAG chair) for ISO 32000 and ISO 14289.
More contributions
Using PDF/UA in accessibility checklists

PDF/UA, like PDF itself, is internally complex, but used correctly, actually makes things easier.

PDF Association expands its board of directors

Catherine Andersz of PDFTron Systems, Alaine Behler of iText Software and Peter Wyatt, ISO Project Leader for ISO 32000 enrich the newly elected board of the PDF Association.

PDF Days Europe 2018 concludes with record number of attendees

Richard Cohn, Principal Scientist at Adobe and the co-author of PDF 1.0, gave the opening keynote at the PDF Days Europe 2018.

Interview with René Treuber, Product Manager of axaio software, about PDF Days Europe 2018

René Treuber, Product Manager of axaio software, will be hosting a presentation titled “Introducing ISO standards for PDF “processing steps” and “print product metadata”” at the PDF Days Europe 2018. In this Interview he gives some background information about it.

Interview with Roman Toda, CTO of Normex, about PDF Days Europe 2018

Roman Toda, CTO of Normex, will be hosting a presentation titled “Encryption with PDF 2.0” at the PDF Days Europe 2018. In this interview he gives some background information about it.

A PDF Page Is a Painting


This article attempts to explain the concept of “reading order” in PDF files. Why is this necessary?

  1. Users are often frustrated by inconsistent and often illegible results when trying to read PDF files on mobile devices, search for PDF content online, or when using assistive technology (AT).
  2. Those tasked with ensuring accessibility or Section 508 compliance often focus on objects rather than logical structure, thus missing the mark.
  3. Software developers are (understandably) confused by “reading order” as presented in today’s PDF Reference (ISO 32000).

Many have come to use the term “reading order” as functionally synonymous with the logical order provided by PDF tags, but this interpretation is incorrect.

A screen-shot showing a simple example of how painting order and logical order may differ.

The PDF Paintbrush

When you create a PDF, you’re painting a picture. Your “paintbrush” is the combined effect of the software used to create the source document and the software you’ve chosen to convert your source document into PDF.

Like brushstrokes, each character, each line and each image is created independently, but interact to produce particular visual effects. On a PDF page, objects are connected by a coordinate system and little else. There’s no logical connection between the letters comprising a word; characters simply happen at a series of locations on the rendered page.

As originally designed, PDF is a system for painting on a page. There’s no innate concept of words, sentences, paragraphs, columns, headings, images, tables, lists, footnotes – any of the semantic structures that distinguish a “document” from a heap of letters, shapes and colors. PDF is fundamentally about how the document appears on the page, not how it looks when abstracted from the page.

(Originally posted on appligent.com. Read the rest of the article there)


Tags: accessibility, logical order, logical structure, reading order
Categories: PDF, PDF/UA