PDF Accessibility
Accessible PDFs are "tagged" PDFs. The tags within a PDF provide a textual representation of the information being visually presented. Properly tagged PDFs are essential for users of assistive technology such as screen readers or refreshable braille displays!
A properly tagged PDF provides assistive technology software with the necessary semantic and structural elements needed to identify, interpret and present the content to the user in a manner which allows them to fully comprehend the context, meaning and relationships of the data being presented.
PDFs can be created from within Acrobat, however more often than not they are created in a different application then converted into a PDF. The accessibility issues that may or may not arise will depend depend on how the source file was formatted as well as how the PDF was created.
For these reasons, it is always wise to have the original source file on hand, if possilbe, should the need to recreate the PDF arise due to aforementioned issues.
The Checklist
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Was the PDF given a decriptive file name?
- Descriptive file names help all users easily locate, open and switch between documents.
- File names need to be different than the title set within the document properties. Assistive technology will read the file name when the document is accessed, if the file name and the title are the same it may lead to confusion for the user as they may think they did not actually open the file.
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Does the text/background, or images of text/background have a contrast ratio of at least 4.5:1?
- Users with low vision and color blindness may have difficulty reading documents that do not present sufficient contrast and color difference between background and foreground elements. Exceptions:
- Large-scale text and images of large-scale text should have a contrast ratio of at least 3:1;
- Decorative images / images of text; including logotypes
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In the document properties, was the document given a contextual title in the Title Field, and was the Initial View set to "Document Title"?
- Contextual document titles allow users of assistive technology to quickly determine if the file contains the information they are seeking without having to read through the content.
- Setting the initial view to document title will tell assistive technology software to read the document title when the document is opened rather than the file name.
- The default view in the settings for PDFs is set to File Name, if this is not changed then users of assistive technology will hear the file name twice. Once when the file is accessed, and again when it is opened. This can cause confusion for the user as it may lead them to open the file more than one time.
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If the document content is not written in the English Language has the appropriate Language been set within the document properties?
- The default language within Acrobat is English. If the appropriate language for the document is not set words may be mispronounced by screen readers, which can lead to misinterpretation of both the meaning and overall concept of the information being conveyed.
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In the document security properties, is "Content Copying for Assistive Technology" allowed?
- If "content copying for assistive technology" is not allowed it may block assistive technology from accessing the content.
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Is the PDF a tagged PDF?
- Untagged PDFs do not provide the necessary semantic and structural elements assistive technology software needs to identify, interpret and present the content to the user.
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Does the PDF contain a Table of Contents? If so, is it properly tagged as a Table of contents? (in the tags pane is there a 'TOC' tag and are there one or more 'TOCI' tags nested under it?)
- Properly tagging the table of contents provides users of assistive technology with the structure and overview of all the topics and subtopics within the document
- Users of assisitive technology can use the table of content links to easily locate and jump to specific sections of the document without needing to skim through all of the documents content to locate the information they are seeking.
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Are all visual headings tagged with Heading Tags and do they follow a logical heading structure (e.g., H1, H2, H3 etc)?
- Assistive technology does not recognize visual text formatting (bold etc), therefore it cannot infer and translate the meaning behind these types of visual cues to the user.
- Headings are used to break up sections of content and they provide a logical structure that the user can use to navigate through PDFs to quickly locate specific sections of content.
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Is each visual paragraph of text with tagged with indiviudal paragraph tags?
- If text containing meaningful information is not tagged as text it cannot be identified as such by assistive technology and therefore will not be conveyed to the user.
- Improper tagging of content, such as tagging paragraphs of text as a list items; or vice versa can lead users of assistive technology to misunderstand the meaning and relationships of the content being presented.
- Visual separation of paragraphs cannot be identified by assisitive technology. Tagging paragraphs of text as they are visually presented provides users of assisitive technology with the structure needed to to determine the meaningful associations between disctinct pieces of content.
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Are all visual lists tagged as lists? If so, are the lists tagged correctly? (in the tag pane, is there a list tag 'L' and is there one or more nested list item tags 'LI' under it)?
- Assitive technology cannot infer meaning from symbols and indentations. Properly tagged lists provide the structure that assitive technology software needs to idenfity, interpret and present the list items to the user in a manner which allows them to fully comprehend the context, meaning and relationships of the data being presented.
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If color/text formatting (bold etc.) was used to convey important information, was the importance of the information conveyed in another manner?
- Importance of information conveyed by using color/text formatting will be unavailable to users of assistive technology.
- Importance of information indicated by color alone will be missed by those using non-color/non-visual displays.
- In addtion, those who experience color-blindness may not be able to dicern the colors used to indicate the importance of the information being conveyed.
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Are there paragraphs of text presented in a different language than the document language set in document properties? If so, is the appropriate language attribute
selected within the paragraph tag properties?
- When the language of a paragraph differs from the document language assistive technology uses the language attribute in the tag properties to provide the appropriate pronunciation for the section.
- If the appropriate language attribute is not set words may be mispronounced which can lead to misinterpretation of both the meaning and overall concept of the information being conveyed.
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Do all images, images of text, charts and graphs that provide meaningful information not conveyed within surrounding text have descriptive alternative text?
- Those with visual impairments, cognitive/learning disabilities often rely on the text based speech output of assistive technology to describe what is visually being presented.
- Alternative text should convey the meaning and concept of the information being presented without the need for visual cues.
- Low-vision users may use screen magnifiers and may have the magnification set to a level which makes it difficult to see an entire image etc. at once.
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Are hyperlinks present within the PDF? If so, are they tagged as actionable links (in the tags pane is there a 'link' tag with a 'OBJR' tag nested under it)? Does hyperlink text convey the
destination?
- Links that do not contain the link OBLR tag are not seen as actionalbe links to assisitive technology, therfore the user will not be able to use the link to navigate to the intended destination.
- Screen Readers contain a feature called a "Links List" which users can use to pull up and navigate to all the links contained within a document. When generic hyperlink text such as "click here" are used users are unable to dicern one link from another within the links list.
- In addition, generic hyperlink text will not provide users of assisitive technology with the intended purpose or destination of the link.
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Does the PDF contain data tables? If so are they tagged as tables with proper structural markup (in the tags pane is ther a 'Table' tag with the appropriate 'TR', 'TH' and 'TD' tags nested under it)?
Does the table markup match the visual representation of the table within the document?
- Tables that do not have proper structural markup will not be fully accessible to users of assistive technology as the relationships between the intented header and data cells is not accurately represented.
- If the structural markup of a table does not match the visual representation of table then the information will not be accurately identified and rendered by assisitive technology in the manner intended.
- Improper table markup can lead to misinterpretation of the data being presented and may lead users to misunderstand the overall concept of the data being presented
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Does the PDF contain form feilds? If so, does each form feild have a unique label and tooltip associated with it? Are the form feilds properly tagged (for each form feild: in the tags pane are there 'Form'
tags with an associated 'OBJR' tag nested under it?
- Each form feild must have a unique label and tool tip that allows assistive technology users to correctly identify the what the form feilds purpose is and enter the correct information being requested.
- The use of generic or repetitive form labelse and tooltips can lead to confusion and frustration for users of assisitive technology as they will not be able to properly identify the intended purpose of each form field.
- Additionally, should changes need to be made to the form feilds the use of generic form feilds and lables will make this task more difficult as the editor will need to manually scroll through the form feild list while looking at the PDF form itself to dertermine if they are editing the correct feild.
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If any audio or video content was embedded into the PDF, were text alternatives (e.g., captions/transcripts) provided and are the audio and video controls accessible?
- Without captions or transcripts for video with audio users with hearing impairments may misinterpret the meaning and context of the visual content being presented. Additionlly, if there is an audio file with no corresponding video then they will miss the content entirely.
- Screen reader users rely on the text based speech output of assistive technology to describe what is visually being presented; therefore although they may be able to hear the corresponding audio the meaning and context of the information being presented may not be clear to them
- If the video/audio controls are not accessible (e.g. labeled) then screen reader users will find it difficult to access and navigate through them.
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Does the PDF contain flashing images?
- If not necessary, flashing images should be avoided or removed as content that flashes or flickers can trigger seizures for some users
- If flashing or flickering images are necessary it should not flash or flicker more than three times per second.
- Please see the W3C formula for calculating general flash and red flash thresholds to test your content to make sure it flashes or flickers at a safe level.
- In addition, flashing or flickering content can be distracting for users with cognitive/learning disabilities and all users in general.