Open and Save Files in Formats Supported by Word
Source: Microsoft Tips
A file format defines the way that information is stored in a file, so that a specific program can open and save that file. A file's format is indicated by a three-letter or four-letter extension after the file name. For example, when one saves a new document in Microsoft Word, Word by default stores the document in Word format with a .doc file extension. Word can directly open and save documents in some file formats. For documents in other formats, Word uses file format converters for opening and saving. The most commonly used converters are installed with Word by default - unless the user or the administrator chooses to make them unavailable on the computer.