Most sites accumulate PDFs — old price lists, brochures, whitepapers, forms — and most organisations have no inventory of them. They are indexable, they rank, and they are invisible in a CMS page list.
Finding them
Filter a crawl export to lines ending in .pdf. The result is usually longer than anyone expects and contains documents from several years ago.
Why they matter
A PDF that ranks is a page representing the organisation with no navigation, no calls to action, and frequently outdated pricing or claims. Some of them attract meaningful traffic, and a few attract links.
Deciding what to do
The ones with traffic or links deserve either an updated replacement or an HTML equivalent that can convert. Genuinely obsolete documents should be removed and redirected, not left to rank quietly with information the organisation no longer stands behind.
Try it: Keep Lines Ending With on SeoWolf's Notepad.