Data files do not contain any executable code, so should not be confused with program files. It should also be noted that data files do not contain any configuration data (system files). A data file should be thought of as a collection of miscellaneous data that is generally intended to be used only by the application.
Applications can store their data so that the content is obscured (referred to as closed or proprietary) or open, allowing a user to view the content if required. Applications generally store their data in either ASCII (plain-text) or binary format.