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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
2018 PDF 2.0 Interop Workshop

Following the success of our previous interop workshops in Cambridge, England and Boston, Massachusetts in 2017, the 3rd PDF 2.0 Interop Workshop is taking place immediately following this year’s PDF Days Europe, in Berlin as part of the post-conferenc …

Post-Conference of PDF Days Europe 2018

On Wednesday, May 16, 2018, directly following PDF Days Europe, the PDF Days Post-Conference offers a variety of workshops on PDF 2.0 Interop or PDF/UA.

PDF Days Europe 2018 – schedule of sessions

Fittingly for the tenth anniversary of PDF’ becoming an ISO standard, standardization will play a significant role this year. The focus will be on recent developments, with an eye on the future. The agenda also includes PDF market analyses, next-generation PDF for mobile devices, universally accessible PDF files and the industry-supported veraPDF validator initiative.

Hotel Recommendations and Sightseeing Tips for PDF Days Europe 2018 in Berlin

You will visit the No. 1 PDF event – the PDF Days Europe 2018 in Berlin? Great! Here are some hotel recommendations and sightseeing tips near the event location (SI Hotel).

A double anniversary for PDF Days Europe 2018

Richard Cohn, Principal Scientist at Adobe, one of the two co-authors of the original PDF specification in the era of Acrobat 1.0 gives the keynote on 25 years of PDF during the PDF Europe 2018.

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