[bingdig]

I've noticed filetype:pdf no longer really works - tons of sites that require you to sign up for an account before seeing the file. Used to be a great method to find pdfs of textbooks / other resources.

[souprock]

Back in the good old days, filetype:exe would actually work.

[scrollaway]

These might be shitty websites which employ black hat seo techniques of serving the pdf to google and a paywall to users.