A File is an object on a computer or collection of records which stores data, information, settings, commands that are used with a computer program. In a graphical user interface (GUI) the Files are shown as unique icons that relate to the program that opens the File. For example the picture is an icon associated with Adobe Acrobat PDF files. If this File was on your computer double clicking the icon in Windows would open that File in Adobe Acrobat or the PDF reader installed on the computer. File must have a .extension which describe the behavior of the File means that what type of File likes .doc, .pdf, .jpg and .ppt etc. All these File extension have different behavior in different environment.