DOC is an extension for word documents with the binary file format. Over 30 years ago, MS Word used the DOC file format. This file format was proprietary and was only supported by MS Word. In the 1990s and 200s, There were other products as well that worked with DOCS files, but the format was not supported in other types of word processors. In 2008 an updated version of DOC was released by Microsoft, which can also be used in other programs with few limitations.