This page is intended to guide faculty who want to learn more about the characteristics of accessible PDFs. Visit Understanding PDF Accessibility if you are just getting started with this topic!
When people talk about “accessible” PDF files, they are usually referring to “tagged” PDF files. PDF tags provide a hidden, structured representation of the PDF content that is presented to screen readers. They exist for accessibility purposes only and have no visible effect on the PDF file. There is more to an accessible PDF file than tags, but an untagged PDF would not be considered “accessible”.
HTML tags and PDF tags often use similar tag names (e.g., both have tags named h1) and organization structures. If you are comfortable with HTML, you will probably have an easier time creating and editing tagged PDF files, but knowledge of HTML is not necessary.
Adobe, Acrobat, and PDF
Adobe, Acrobat, and PDF are often used interchangeably, but they are not the same. The relationship between these terms is similar to the relationship between Microsoft, Word, and DOC(X).
- Adobe is a company; they are the creators of PDF (the format) and Acrobat (the product).
- Acrobat describes a series of tools created by Adobe for viewing, creating, and editing PDF files.
- PDF is a format or type of document. Its main purpose is to preserve the formatting of a document. It was created by Adobe but is now an open format that can be created and displayed by other programs.
There are 3 Acrobat Tools:
- Acrobat Reader allows user to view and interact with a PDF (including the accessibility features of a PDF), but it cannot be used to create new PDFs or edit existing ones.
- Acrobat Standard adds the ability to create a PDF, along with other features like converting a scanned PDF to a searchable file. However, you cannot view or edit accessibility information.
- Acrobat Pro is the only version of Acrobat that can be used to view and edit the accessibility information of a PDF. The Adobe Creative Cloud software suite is available for DU faculty and benefitted staff. Acrobat Pro is part of the suite. Content creators can use the Action Wizard and Accessibility Checker to lead them through creating accessible PDFs.
Top 8 Characteristics of an Accessible PDF
1. Searchable text
A document that consists of scanned images of text is inherently inaccessible because the content of the document is images, not searchable text. Assistive software cannot read or extract the words, users cannot select or edit the text, and you cannot manipulate the PDF for accessibility. Convert the scanned images of text to searchable text using optical character recognition (OCR) before you can use other accessibility features with the document.
2. Alternate text descriptions
Screen readers cannot read document features such as images and interactive form fields unless they have associated alternate text. Screen readers can read web links; however, you can provide more meaningful descriptions as alternate text. Alternate text and tool tips can aid many users, including users with learning disabilities.
3. Fonts that allow characters to be extracted to text
The fonts in an accessible PDF must contain enough information for Acrobat to extract all of the characters to text for purposes other than displaying text on the screen. Acrobat extracts characters to Unicode text when you read a PDF with a screen reader or the Read Out Loud feature. Acrobat also extracts characters to Unicode when you save as text for a braille printer. This extraction fails if Acrobat cannot determine how to map the font to Unicode characters.
4. Reading order and document structure tags
To read a document’s text and present it in a way that makes sense to the user, a screen reader or other text-to-speech tool requires a structured document. Document structure tags in a PDF define the reading order and identify headings, paragraphs, sections, tables, and other page elements.
5. Interactive form fields
Some PDFs contain forms that a person is to fill out using a computer. To be accessible, form fields must be interactive to let the user enter values into the form fields.
6. Navigational aids
Navigational aids in a PDF include links, bookmarks, headings, table of contents, and preset tab order for form fields. Navigational aids assist users in understanding the document without reading completely through it. Bookmarks are especially useful and can be created from document headings.
7. Document language
Specifying the document language in a PDF enables some screen readers to switch to the appropriate language.
8. Security that doesn’t interfere with assistive software
Some PDF authors restrict users from printing, copying, extracting, adding comments, or editing text. The text of an accessible PDF must be available to a screen reader. You can use Acrobat to ensure that security settings don’t interfere with the screen reader’s ability to convert onscreen text to speech.
For more information about PDF accessibility, visit the Acrobat Accessibility Series.