Dropbox provides a feature that allows you to get the URL of a stored file and then, you can send the link to third-parties. It's simple and convenient but have you ever taught that this means that anybody can access that file if somehow they can guess its URL?
However, Dropbox links do not reveal who shared the file. There is no way to find back the account owner, except if personal information is disclosed in the shared file. Anyway, keep in mind that shared files can be read by anybody! This feature must be used with due care and attention. It is recommended to encrypt sensitive data before sending it to Dropbox.