To a different program, this data is gibberish, and often the application will simply display an error message and refuse to load the file. If you do manage to load an unsupported file, it might appear on the screen as unformatted text or as junk, or it might even crash the application and perhaps the operating system as well. A file created in WordPerfect 8.0, for example, contains not only the text typed by the author but also formatting codes for elements such as fonts, margins, tables, graphics, and styles, specified during the document's creation. Word 2.0 can't follow the WordPerfect 8.0 formatting instructions and thus will load the file as gibberish, if at all. Word 97 and 2000 will load the file by converting it from WordPerfect format into Word format using a conversion utility built into the application.
Every file format is identified by an extension added onto the file's name.
In the operating system, file extensions are associated with applications that can work with them, so that double-clicking on a file icon causes the file to be loaded into the correct application. How the most common image file formats store pictures. Fix Windows file association problems.