What triggers automatic cache purge?

Hi Folks- i’m wondering if you can clarify what constitutes ‘changing the appearance of your website’?
Just curious as i’m currently wasting an inordinate amount of time each week replacing slightly altered PDF files on a bunch of sites (updated floor plans for events which need to maintain the same filename and URL due to the direct link being shared by email a lot) which has always involved going in and clearing the cloudflare cache between deleting the old file and uploading the new one.

Could you let us know what circumstances or actions would cause the plugin to automatically clear the cache?

Many thanks,
Pete