| PDF
files can contain many things. At a minimum, a PDF contains the text, graphics,
bookmarks, links and other elements of content that go to make up an electronic
document. In
addition to content, PDF files may also include "structure". Structure is the
set of instructions that define the logic that binds the content together - the
correct reading order, for example, and the presence and meaning of significant
elements such as headings, figures, lists, tables, and so on. It
is structure that makes PDF files usable by those who must use assistive technology
(screen readers and the like) to read files from a computer. In
PDF files, logical structure is expressed via "tags". Tags may be generated automatically
for any PDF file using Acrobat Professional, but unless the document is very simple
indeed, automated tagging alone is unlikely to produce satisfactory results, and
is certainly not a quick-fix for compliance with Section 508. A
PDF file equipped with quality-controlled tags may be read using a screen-reader
or other assistive technology that reads PDF tags. If the PDF file is also optimized
for Reflow, then it will read well using assistive technologies that do not use
PDF tags, as well as on mobile devices. Adobe's
Acrobat Professional will add tags to a PDF file, but human intelligence is still
required to ensure the tagging process was performed correctly. There is little
room for error in document tagging. Even seemingly small errors in document structure
can easily render a file completely incomprehensible. Imagine
using your computer with the screen turned off, and you'll get some idea of how
important logical text-flow is to anyone who needs a screen-reader to read your
PDF! Characteristics
of a fully accessible PDF include: - A
logical reading order has been established for all page content
- Tags
have been created and validated for all logical content
- Images
are given correct alternate descriptions
- Tables
are correctly tagged to represent the table structure
- Form-fields
are authored to promote their utility to screen-readers
- Represents
text as Unicode to clear up composition irregularities such as soft and hard hyphens
First
published on Planet
PDF, this article has been updated for this website. Non-commercial reuse
is permitted only when attributed to Duff Johnson, Document Solutions, Inc. www.document-solutions.com. | 
