PDF was originally intended to serve as electronic paper; a properly rendered page irrespective of software or operating system. Pages, however, aren't just for reading. Since people like to add notes, draw lines and fill forms, Adobe Systems, the inventors of PDF, decided to cater to these uses as well. PDF rapidly accumulated new features beyond faithfulness to the rendered page it began to mirror the interactive capabilities of real paper.
The first generation of interactive PDF features consisted of annotations of various types. Some allowed users to add text, others allowed users to draw lines and boxes onto the page. Still others go beyond the paradigm of the page, making it possible to add hyperlinks, audio and movies to PDF.
The second generation of interactive PDF brought the ability to deploy a PDFs content outside the page-based world.
Tagged PDF provides the means to effectively deploy a final-form document to a mobile device. Its the same means by which PDF files may be made accessible to users who requires Assistive Technology (AT) to read.
One of the primary motivations for tagged PDF was to achieve compliance with regulations that require electronic documents to be accessible to users with disabilities, but implementers can leverage tagged PDF to accomplish or enhance a wide range of end user activities.
The following table indicates the utlity of untagged vs. tagged PDF content.
|Untagged Content||Tagged Content|
|No semantic types or ordering; content is ordered solely for rendering purposes||Semantic type and order is determined, content may be reused accordingly|
|Search engines cannot reliably access words and phrases||Search engines get reliable access to content.|
|No reliable means of reflowing page content onto smaller devices||Includes information necessary for reflow|
|Real content and artifacts arent distinguished||Consuming software can choose to utilize or ignore artifacts|
|Content copying and extraction is unreliable||Content may be extracted with confidence|
|Not eligible for PDF/A conformance level A||May conform with PDF/A conformance level A|
|Cannot comply with WCAG 2.0 or Section 508||May comply with WCAG 2.0, Section 508 and other accessibility regulations|
|Inaccessible to disabled users||Accessible to those with PDF-aware Assistive Technology|