Just for clarity, we can only check if links are actually entered in the document. If there is simply a URL in the text of the document and it is not actually linked, we cannot test in that situation.

Bookmarks are used in PDFs to help allow users to jump directly to important sections of documents. Users of assistive technology will find it difficult to use documents without bookmarks, especially if the documents are long or do not have tags.
​More information on bookmarks check

Users of screen readers rely on correct markup for tables to understand the information that is provided. If it is not possible to determine the context of the table entry, then the information contained within the table will not make sense.
​More information on table element usage

Heading elements should be used in the correct order to help users using a screen reader to navigate the document.
​More information on heading tag usage

Link text in PDF documents should be marked up to be recognizable by keyboard and assistive technology users. That is, the link information is programmatically available to user agents so that links are recognizable when presented in a different format.
​More information on link annotation usage

Form fields should be marked up correctly to help users identify what kind of data is expected from them.
​More information on form field mark up

Replacement link text should be provided via the /Alt entry in the property list for a tag. This is usually not necessary, but in some situations, additional information beyond the visible link text is needed, particularly for screen reader users.

More information on using Alt entry for links

A mechanism should be provided that allows users to explicitly request a change of context using the submit-form action in a PDF form.

More information on using submit-form action in forms

Not having consistent page numbering in a document makes it challenging for navigation. If the page numbering used by the PDF viewer control differs from the numbering on the pages, users can not navigate to the referenced pages by entering the page number in the PDF viewer control.
​More information on providing consistent page numbering

Whenever an image is presented without an alternative text, it causes challenges for users that are blind or have vision impairments. Any information conveyed in an image is lost to these users whenever a textual alternative is missing.
​More information on text alternatives for images

If the tab order is not correct within a document, users that utilize assistive technology may not be able to understand the content.
​More information on correct tab and reading order

Headers and footers help make content easier to use and understandable by providing repeated information in a consistent and predictable way.
​More information on running headers and footers

Screen reading software uses the default language to determine how it will pronounce text. The reader can distort certain words if the language is not correctly set.
​More information on setting the Lang entry

Document titles help to quickly communicate the purpose or topic of a document. If a title is not available, the user will need to take more time to determine if the information is relevant.
​More information on setting the Title entry