Integrating Accessibility into PDF Documents
It is essential when creating digital resources to make them accessible for those who struggle with text, and Adobe's Portable Document Format (PDF) is a great resource for displaying digital information online as well as offline. Generally there are two approaches to making PDFs accessible.
Image Only PDFs are documents that are complete scanned images, which are inaccessible because no real text information is available. With the help of Optical Character Recognition (OCR) software, we can extract this information into a text format. There are many free OCR software options available; however, there are some limitations associated with the use of OCR. Sometimes OCR fails to understand signature images, math or chemistry formulas, or non-English characters.
Tagged PDFs have a real document structure. These PDFs have the information that says this content comes before that content, and you can mark up that information with headings, image descriptions, table information, etc. To achieve these results, there are many options available as well, with Adobe Acrobat Pro being the most recommended.
When creating an accessible PDF document, make sure that the title of the PDF is unique and descriptive. The correct heading structure used in PDFs should start with H1. Verify that bookmarking is followed using a logical reading order. Since the use of lists is common in PDFs, check whether the correct tagging is used. Tables can play a significant role in representing data relationships, so make sure they include row and column header tags.
You can incorporate more support for PDF forms by using tags and adding information so that someone using assistive technologies can actually interact and complete the form independently.
If graphic images are used, appropriate alternative text needs to included for all images (except decorative) that is easy to read for screen reader users. If pie charts, graphs, model charts, etc. are used in PDFs, more detailed information should be included. The use of multimedia is increasing in PDFs, so these elements should be made accessible for users as well.
As for the basic page elements, if there are any internal or external links available on the page, make sure they are easy to find and that their purpose is conveyed to users. Select the appropriate font size, provide spacing between paragraphs to increase readability, use a logical tab order, and make sure users can easily scroll up and down the page.
From the perspective of those with impaired vision, a good contrast ratio is needed for PDF document text. Color alone should not be used to represent information; make sure the same information is also conveyed through text. Check the zoomed in view on pages for any potential loss of content or functionality. If security features are included, make sure they are compatible with assistive technologies.
Regardless of which software you use to make PDFs accessible, you need to be sure that your documents are correctly structured and that you produce reliable, accessible results for everyone.