A free papers search engine
Your friend is probably thinking of Sci-Hub. Warning: it's likely illegal, including to use the service (as opposed to uploading stuff onto it), in most jurisdictions. If it's not already illegal in your jurisdiction, the trend is towards illegality (i.e. lawsuit after lawsuit has been ruled on, and they are usually in favor of the copyright holder).
If you want to do things legally, try something like Unpaywall, or ask your local librarian. Librarians are incredibly good at finding papers, and they can often access something for free even if you can't.
In addition to Sci-Hub and Unpaywall mentioned by Allure, there are also databases for scientific papers which were published legally with an Open Access license, such as CORE an BASE.
I would also add to the above the very commonly used resource Library Genesis, which is less for paywalled papers and more for pdf's of books, including textbooks, but do keep in mind that this definitely falls in the same legal gray area as Sci-Hub and things like torrenting copyrighted materials.