Native file format
The native file format is a method used by the computer operating system or file management to arrange data. For example, when you save a Microsoft Word document, the data in the file is customized and optimized to be read in Microsoft Word. These files have the .doc or .docx file extension.
Most native file formats are distinguished by the user by the file extension.
Native file formats allow a program to distinguish the type of file and how to display that file when opened. If a file is unrecognized, it will be unable to display the file or not display the file properly.