They have the datetime they were saved, and the filename is usually derived from the page title - this often needs a bit of manual tweaking on my part if the original author hasn't named it something sensible, but its a minor action to take. Every year or so I 'sanitize' the filenames of the archives, to make sure I can still search them with normal command-line (bash) tools, removing special % ^ # $ & chars, and so on ..

A lot of other info is stored in the PDF metadata, too ..