How can I access the directory listing of a website (as a visitor not an owner) to download pdf files that I need and that are hidden by their owner

I downloaded a file from this link "https://example.com/documents/courses/philosophy/lecture1.pdf then I wanted to access all files in that folder(philosophy) so I typed this: "https://example.com/documents/courses/philosophy" but it says page is not working. I tried to guess other pdf documents but it didn't work. Any solutions?