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The outline of a PDF file allows screen readers to easily navigate a document.  For instance, if every section of a chapter is tagged, a user can quickly jump from one section to the next.  Microsoft Word documents created using the built-in heading styles (e.g. Heading 1, Heading 2) can be used to create tagged PDFs than contain an outline.  PDF created from a scanned document usually do not have outlines because the scanner cannot distinguish between chapters or sections with a document.  It can be complex to tag PDF files. 

Symbols

The following symbols are used to display the result of the accessibility file scan.  

A green check means the test passed

A red X means the test failed

An orange exclamation mark means that the PDF is partially accessible

A blue question mark means that the file has not yet been scanned or the file has an error which prevents it from being scanned.  The file could be corrupted or have a password which prevents the tool from opening the PDF.  

How to Fix PDF Files

Check with the Library

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