Here a software product that is used to make up your secret file so as to let other people can't recognize your secret. Do not hide. Your files still exist in disk, but your friends or colleagues can't recognize what files it is and can't read it by any other tools unless the original program. Your secret file such as photo, word or pdf file, video or audio file, cartoon file etc. How do you think of such program product?
Difficult to say with such limited info. Would it be indexed by google desktop search or similar programs? Is it encrypted? Encrypting a zip archive also limits access to the file, maybe that's enough.
all such file extensions provide encryption in some way so u need to use that but if you want to combine all features in one may be u need to make your own new file extension with supporting software for that or make a zip and encrypt but decrypting opening the file will be problem