Tell you more about from that era.
A more dangerous reason for dual extensions is malware distribution. While .epub files are generally safe text documents, bad actors often used similar dual-extension tricks (like .avi.exe or .avi.vbs ) to hide executable viruses. If a user’s operating system is set to "Hide extensions for known file types," a file named video.avi.exe will simply appear as video.avi . Clicking it runs a program instead of playing a video. The Cultural Context: Brasileirinhas and Carnaval 2006
Be wary of any file that lists two different media types in its name (e.g., a "video" ending in a "book" format).
Carnaval 2006: Dirigido por Jose Gaspar. Com Gabriella Asstryd, Babalu, Carlos Bazuca, Veronica Bella. Carnaval 2006 (2006) — The Movie Database (TMDB)