(DOCument file) A file created in a version of Microsoft's word processing application prior to Microsoft Office 2007. DOC files use a .DOC extension and differ from text files (.TXT extension) because they contain proprietary codes that must be opened in Word or software that reads the Word format. Although Microsoft Word 2007 reads and writes DOC files, its default document format is entirely different (see Office Open XML).A De Facto StandardSince Microsoft Word has been used by so many Windows and Mac users, the DOC file has become a de facto standard for communicating textual information and is routinely sent from one user to another as an email attachment. Contrast with ASCII file. See Microsoft Word and PDF.