doc The .doc filename extension is a native file extension used by the closed source document processing application Microsoft Office Word. Initially developed and used by Microsoft since 1983, the filename extension .doc continues to be supported natively even in the most recent iteration of the word processing application Microsoft Office Word 2013. The more recent .docx filename extension however was introduced by Microsoft in Office Word 2007, becoming the default filename extension. Documents to be saved in the .doc format are saved as Word 97, 2003 documents.
odt The Open Document Text filename extension format is an alternative open source document and text processing file format allowing users to create text documents that can be opened and edited by an extensive list of document processing applications. Both proprietary applications (such as in Microsoft Office word) and open source document processing applications (such as OpenOffice) support the .odt filename extension allowing for interoperability between software systems. The format is useful to those creating documents meant to target a wide audience and not necessarily an audience with a specific document processing suite. The extension was first released in 2005.