: Web developers use unique hashes in filenames to force browsers to download the most recent version of a file rather than loading a previously cached version.
: Randomly generated tokens or hashes (like x6gu2rn29o1b ) are often used by websites to prevent users from guessing direct download URLs or to control access through unique session tokens.
An EPUB (Electronic Publication) is the industry standard for digital books, designed to be "reflowable," meaning the text automatically adjusts to fit different screen sizes. .EPUB Files - What They Are & How to Open .EPUB - Adobe