User`s guide

Accessing PDF Documents with Assistive Technology 11
Types of PDF Documents
Before your screen reader can access an image only PDF document, you need to convert the image
into accessible text. You can use any application with built-in OCR functionality, including Adobe
Acrobat. You can also use certain third party OCR soware applications, which have built-in tools to
recognize PDF les. Even with the best OCR technology available, the result may not be perfect. If
none of these tools are available, or if you cannot prevail upon the original author to correct the
situation, you may need to obtain sighted assistance to have the document read to you.
Untagged documents
PDF documents oen contain page layouts with multiple columns, sidebars, and captions for photos.
As a result, even when a PDF contains actual text instead of images only, it may be inaccessible because
of problems in determining the most appropriate reading order. A screen reader might not be able to
extract words, sentences and paragraphs in a coherent order. Instead, they may be mixed together in
disconnected, confusing ways. For example, when the text of a PDF le is arranged in columns like in a
newspaper, the structure of the document is apparent visually, because extra spacing or border lines indicates
where one column of text ends and another begins. Screen readers, however, cannot always detect these
visual cues. In these cases, information about the document structure must be included in the PDF le
for a screen reader to present a document in an intelligible manner. Without structural information that
groups and separates regions of the page, the document may be inaccessible to screen reader users.
PDF tags are used to address such accessibility problems. PDF tags are similar to tags used in HTML to make
Web pages more accessible. e World Wide Web Consortium (W3C) did pioneering work with HTML
tags to incorporate the document structure that was needed for accessibility as the HTML standard evolved.
For example, a phrase may be tagged as the heading of a section, the caption of an image, or a cell within a
table. Some tags are necessary for proper visual display in a web browser, but other tags are recommended
specically to aid accessibility. Accessibility tags may include an indication of the row and column labels
of a table, which enables a screen reader to tell the user about the context of each cell. e cell information
may be useless or confusing without knowing the associated row and column labels. When authors fail to
use tags to indicate the internal structure of the document, the PDF documents they create are untagged.
Unfortunately, you will likely encounter many untagged PDF documents, making
it dicult for your screen reader to make sense of the document.
Automatic tagging helps alleviate the problems caused by untagged PDF documents. Adobe Reader can
analyze an untagged PDF le and add temporary tags to optimize its reading order for screen readers.
When you open an untagged PDF, Adobe Reader presents a dialog box that allows you to choose the type of
tagging you want it to perform on the document. e tagging process can take a few minutes for large les,
so your screen reader will alert you that the document is being processed while it is being tagged. When the
tagging is complete, your screen reader will begin reading the document. e le is only tagged temporarily
-- because the tags are not saved, the process will have to be repeated if you open the document again.