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A PDF file stores information about the language of the document. This is used by screen readers and other assistive devices to ensure proper pronunciation and is particularly important for documents that are in foreign languages. See: Changing the global language of an Adobe PDF | Swarthmore ITS Solutions.
Text
If a PDF file does not have text, the file has been scanned as an image. This means that screen readers and other assistive devices will not be able to read the content. As of fall 2023, our current goal is to strive for green checks under both the "Text" and the "Tagged" columns on all documents (except where files are legitimate images not images of text).
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