Fix the reading and tab order in PDFs
A PDF stores a tag order for reading and a tab order for form fields and links, and both have to follow the logical order of the content. W3C publishes PDF3 as a sufficient technique, so getting both orders right satisfies the rules it is filed against, and it is one route among several. Reading order comes from two places, which is why it goes wrong. The tag order sets the sequence of elements, and the content tree inside each tag sets the sequence within one. Multi-column layouts and visually assembled forms often store content in the order it was drawn. Acrobat Pro's Reading Order tool repairs the tags, and the page setting "use document structure" repairs the tab order.
How we find it in an audit
We read the PDF start to finish with a screen reader and watch whether columns, sidebars, and form fields arrive in a sensible sequence. We also tab through every field and link, and inspect the tag tree in Acrobat's Tags panel. The page properties tell us a lot on their own. Tagged documents should be set to use document structure, and a page left unspecified tabs through form fields first, then links, then comments in row order, which is almost never what the layout implies.
How affected users experience it
When the order is wrong, a two-column statement reads as interleaved nonsense. One line from the left column, one from the right. In a form, Tab jumps from name to the signature block and back up to date of birth. The content is all there, but scrambled.
Passes vs. fails
Passes
The form's tab order is set to follow the document structure, and the tag tree matches the visual layout. Name, address, date of birth, then signature, which is the same order a sighted person fills it in.
Fails
A benefits application form tabs through fields in the order they were drawn. Applicant name, then the office-use box at the bottom of the page, then back up to address.
How this gets tested
The W3C publishes test rules that define what a checker looks for here.
- Iframe with interactive elements is not excluded from tab-orderA tool can check this
- Scrollable content can be reached with sequential focus navigationA tool can check this
Other ways to satisfy this rule
12 guides on this site are filed under 1.3.2 Meaningful Sequence. W3C lists this one as sufficient for that rule on its own. Implement it correctly, in a way your readers' software actually supports, and the rule is met.
- C6sufficientKeep source order meaningful when CSS repositions content
- C8sufficientSpace letters with CSS, not blank characters
- C27sufficientMatch DOM order to visual order
- G57sufficientPut content in a meaningful reading order
- H34sufficientKeep mixed-direction text reading in the right order
- H56sufficientFix nested right-to-left text with the dir attribute
This guide is our interpretation of W3C technique PDF3: Ensuring correct tab and reading order in PDF documents. W3C publishes its techniques as guidance rather than as the standard, and says so on every one of them. The success criterion is what conformance is measured against, and a technique is one documented way to meet it.