On a similar topic, PoC||GTFO [0] features files that are valid with multiple file formats. Issue 19 [1], for instance, "is valid as a PDF document, a ZIP archive, and a HTMLpage. It is also available as a Windows PE executable, a PNG image and an MP4 video" (see "technical note").
They are made by Ange Albertini [2] who has a great talk [3] on how he does this kind of things
[0] https://www.alchemistowl.org/pocorgtfo/ [1] https://www.alchemistowl.org/pocorgtfo/pocorgtfo19.pdf [2] https://github.com/angea/pocorgtfo [3] https://www.youtube.com/watch?v=W9WnnMJ0RKg