Every file that has, or ever can exist, is just a different combination, and length of a pre-defined set of characters. Because of this, any file can technically be created by generating combinations of characters, provided there's some way to identify that combination when reached. In most cases, generating files in this manner is not realistic, because of the sheer number of combinations that would need to be explored. Even if you dedicated your life to it. However, extremely small pieces of data (e.g., "Hi") can practically be generated in this manner. If an upload has been removed from this website, but was extremly small in size (a few bytes), you may be able to re-create it by brute-forcing its checksums.