So there are different ways it archives a webpage.

It currently stores the full webpages as a single html file, a screenshot, a pdf, a read-it-later view.

Aside from that, you can also send the webpages to the Wayback Machine to take a snapshot.

To archive pages behind a login or paywall, you can use the browser extension, which captures an image of the webpage in the browser and sends it to the server.