PDF Accessibility Principles
Considering accessibility is important both when creating a PDF and when publishing a PDF on the internet.
Requirements for PDF accessibility include, but are not limited to:
- PDFs should always have an accessible alternative, such as HTML, Word, Text, or RTF;
- PDFs must be tagged with accessibility features, such as:
- Headings and text;
- Alternative text for images;
- Tables and lists;
- Bookmarks; and
- PDF forms must be coded with accessibility techniques;
- Page numbers must be specified for consistency across PDF readers;
- The document title and language must be specified;
- Bookmarks must be used in addition to headings to navigate content; and
- All text must be searchable (i.e. the PDF is not a scanned image).
Requirements for HTML accessibility include, but are not limited to:
- PDF should be published with an equivalent accessible alternative (HTML, Word, Text, or RTF);
- The link to the alternative version must be placed adjacent to the PDF link;
- PDF (and its alternative) link text must:
- be purposeful, descriptive, and meaningful;
- indicate the target is a PDF;
- not use ASCII characters, ambiguous words (e.g. ‘more’, ‘here’), or device-dependent words (e.g. ‘click’); and
- be consistently presented for all downloads.
Impact on Users
PDFs cannot be fully accessible yet because they lack all the features of HTML. For example, the tagging features within PDF are not available to screen readers on mobile and tablet devices. That’s why an equivalent fully accessible document should accompany PDF.
That being said, developers can implement specific features within a PDF to optimize access for people with disabilities, especially for people who are blind or have low vision.
PDF Accessibility Features
Tagging content elements within a PDF creates a logical document structure for assistive technologies to interpret. Having a logical structure means users can understand the reading order of the document and receive extra information about content, such as text, images, and tables.
Non-tagged PDFs are unreliable. They may cause assistive technology to encounter incorrect information, an incorrect reading order, or content that may not be read at all.
How to set tags
- Open the tags panel by selecting the ‘Tags’ icon from the Navigation panel options on left-hand side (if not visible right-click to add to navigation panel).
- From the Tags options, select ‘Highlight Content’ to ensure selected tags in the document are highlight when selected.
- Go through the tags and select those that contain no information. When you select a tag, it will be highlighted in the content section.
- Right-click the relevant tag and select ‘Delete Tag’.
- Re-order the tags so the reading order of the tags matches visual order. Where the order of the tags does not match the visual order, select the tag in the left-hand panel and drag it to its correct position.
- For items that have been tagged incorrectly, in the Tags panel, right-click the tag you want to change, and select Properties. In the Tag tab, select the correct tag type from the dropdown list ‘Type’.
- For documents that are untagged, tags can be added automatically. In the Tools panel, expand the Accessibility options and select ‘Add Tags to Document’. Tags will be added to the document. The progress indicator will show when this is completed.
Tags that can be used:
- Text: Tags the selection as text.
- Figure: Tags the selection as a figure. Text contained within a figure tag is defined as part of the image and is not read by screen readers.
- Form Field: Tags the selection as a form field.
- Figure/Caption: Tags a selected figure and caption as a single tag. Any text contained in the tag is defined as a caption. Useful for tagging photos and captions and preventing caption text from being incorrectly added to adjacent text blocks. Figures may require alternate text. Note: This option will delete the alternative text that was converted from Word.
- Heading 1, Heading 2, Heading 3, Heading 4, etc: Tags the selection as a first, second, or third level heading tag. You can convert heading tags to bookmarks to help users navigate the document.
- Table: Tags the selection as a table after the selection is analyzed to determine the location of headings, columns, and rows.
- Cell: Tags the selection as a table or header cell. Use this option to merge cells that are incorrectly split.
- Formula: Tags the selection as a formula. Because speech software may handle formula tags differently from normal text, you may want to add a description using alternate text.
- Background: Tags the selection as a background element, or artifact, removing the item from the tag tree so that it doesn’t appear in the reflowed document and isn’t read by screen readers.
- Table Editor: Automatically analyzes the selected table into cells and applies the appropriate tags. The table must be tagged as a table before you can use the Table Editor command on it.
Logical reading order
Screen readers and other assistive technologies require a logical reading order or structure to move through the document in an order that is consistent with the meaning of the content.
How to set the Reading Order
- Select the ‘Z’ icon from the Navigation panel options on left-hand side (if not visible right-click to add to navigation panel). The Reading Order panel will appear on the left-hand side.
- In the Reading Order panel, right-click the name of the document and select ‘Show reading order panel’.
- Change each of the following options to different colors:
- Show page content order;
- Show table cells;
- Show tables and figures.
- Select any empty items in the Reading Order panel and right-click (non-content items such as decorative images should also be set to background).
- Select the ‘Tag as background’ option.
- Drag and drop items on the left-hand side so the reading order matches the visual order.
- Where the order does not match the visual order, select the appropriate item in the left-hand panel and drag it up or down to its correct position.
Text descriptions for all meaningful images (ALT text)
Screen readers cannot interpret images such as graphs, diagrams, and scanned text. Alternative text communicates the image content or purpose to users of screen readers or users with a cognitive disability. Images of scanned text are inaccessible because assistive technologies cannot read or extract the words from them. Additionally, text is unable to reflow, which means the text is unable to wrap, or adjust on zoom. Scanned images are also not searchable when a user is looking for information in the document.
How to set text descriptions for images
- Select ‘Content Editing’ in the ‘Tools’ panel on the right-hand side and then ‘Edit Text & Images’.
- Click on the relevant image. The image will appear with a thin blue border.
- In the ‘Tools’ panel on the right-hand side, select ‘Accessibility’ and then ‘TouchUp Reading Order’. A dialog box appears and the mouse changes.
- Very carefully, click and drag to select the entire object. Ensure you select just outside the blue border. Ensure you do not include anything else in your selection.
- When you have successfully selected an object, the buttons in the TouchUp Reading Order dialog box will become active.
- Select Figure, which tags the selection as a figure. Text contained within a figure tag is defined as part of the image and is not read by screen readers. The image will appear in the Reading Order and will be highlighted on the page. Note: non-content and decorative images should be set as a Background.
- Add alternative text
Tables that use the appropriate markup tags
Data in a table must be presented in a way that preserves the relationship of content in different cells, even when users cannot see the table or the presentation format. Using table markup tags conveys to the screen reader the logical relationship between text, numbers, images, or other data that are represented in columns and rows of the table.
How to code data tables
- To determine whether data tables have coded table headers, you must open the Tags panel in the Navigation panel. Review the table headers and data cells to check they are correct.
Changing TD to TH
- Open the Tags panel in the Navigation panel. Expand the tags until the top row of the table is fully expanded.
- Right-click the ‘TD’ in the right-hand Tags panel that needs to be changed to a TH.
- Select ‘Properties’.
- In the dialog box, select ‘Table Header Cell’ in the Type section.
- The table cell will appear as a table header in the Tags panel in the Navigation panel.
- Sometimes several cells have merged to create one table header cell (TH). Open the Tags panel in the Navigation panel on the left-hand side. Expand the Table tags.
- Right-click on the text of the merged TH cells. Select ‘Delete Tag’. Do not delete the TH tag.
- Select the correct text in the document.
- Right-click the relevant TH tag and select ‘Create Tag from Selection’. The tag is created.
Bookmarks and heading tags
Bookmarks and heading tags allow users to locate content more easily by providing a hierarchical outline of the document content, rather than reading through many pages. This outline is especially useful to a person with a cognitive disability or a screen reader user. Bookmarks benefit all people by providing users with a mechanism to go directly to the page or section they want.
How to code Bookmarks
- Open the Bookmarks panel. Select the ‘Bookmarks’ icon from the Navigation panel options on left-hand side (if not visible right-click to add to navigation panel). The Bookmarks panel will display on the left-hand side of the page.
- Go through the bookmarks and select those that contain no information. When you select a bookmark, it will be highlighted in the content section.
- Right-click the relevant tag and select ‘Delete Bookmark(s)’.
Re-order the bookmarks
- Drag and drop the bookmarks on the left-hand side so the bookmark order matches the heading order.
- Where the order of the bookmarks does not match the heading order (see Figure below), select the bookmark in the left-hand panel and drag it to its correct position.
- Sometimes headings do not have a corresponding bookmark.
- Select the text that needs to become a bookmark.
- Right-click the text and select ‘Add Bookmark’.
- The bookmark will be created in the left-hand side.
Changing the nesting of bookmarks
- Sometimes the bookmark is added at the incorrect level. Bookmark nesting should mimic heading nesting.
- Select the relevant bookmark.
- Drag it up or down to the correct location.
Documents with additional navigational aids such as a table of contents provide an easy way for users to move around a document and scan pages for information. Page numbering provides a mechanism for users to orient themselves and find information and is consistent across different PDF readers.
By identifying the language of the document, assistive technologies and conventional user agents can render text more accurately. Screen readers can load the correct pronunciation rules, and visual browsers can display characters and scripts correctly. As a result, users with disabilities are better able to understand the content.
How to set Document Language
- Open the ‘Advanced’ tab.
- Under the ‘Reading options’ section select the ‘English’ option for ‘Language’.
Providing name, role, state, and value information for all form components allows assistive technologies to gather information about and interact with form controls in a PDF. Form components may include text input fields, checkboxes, radio buttons, combo boxes, list boxes, and buttons. Without this information, assistive technology users may not be able to control form fields.
In addition, screen readers can interpret form fields with tooltips to provide extra information.
Most PDF security settings are not compatible with assistive technologies and will prevent access to the document content. Text access for screen reader devices should always be enabled and/or security settings be set to ‘no security’.
Support for PDF accessibility features over various assistive technologies is varying and incomplete. Some features convey semantic meaning that is not supported by all assistive technologies (such as screen readers). For example, a tagged heading allows a user to navigate the sections of a document quickly, and a tagged paragraph identifies paragraph blocks.
These features are not yet consistently supported and therefore an equivalent accessible alternative (HTML, Word, Text or RTF) must also be published, with a link to the alternative next to the PDF link.
Users should be able to understand the purpose of each link so they can decide whether they want to follow the link.
- A list of links on a page can be provided by some assistive technology, and descriptive link text will help users select a link from this list.
- Keyboard users are able to tab from link to link and understand the purpose of the link.
- Descriptive link text helps inform users of the content to expect and the format it may be presented in (e.g. a downloadable document such as a PDF or Word document), enabling them to make an informed choice prior to selecting the link.