IANAL Fair use usually applies to copying the work or publishing it, or making a dervied work from it (y'know all the thing that the copyright holder usually on

IANAL Fair use usually applies to copying the work or publishing it, or making a dervied work from it (y'know all the thing that the copyright holder usually only has legal rights to do). Merely transforming the work yourself and keeping it yourself, wouldn't really count as anything that copyright law has any say over. Since it's not explicitly illegal, it's legal. You don't need 'fair use rights' when you tear up a book in frustration, or your kid scribbles on it. Likewise you can copy your file locally and mangle it if you want. Copyright law only gives the copyright holder some rights to some things. It's not like they own every single copy of the book/film/file completely. This is why there was a new law in the USA (the DMCA) which explicitly criminalized breaking DRM. They needed a new law for it. (However you may enter the territory of hacking a computer system (which is broadly "doing something to a computer that the owner doesn't want").