docx In an effort to create an open document standard, Microsoft in collaboration with ISO/IEC and Ecma, developed the Office Open XML standard in 2006. One of the filename extensions supported in this specification is the .docx extension, a text document filename extension. The .docx was introduced in Microsoft Office Word 2007 and has been supported ever since in later iterations. It has become the default filename extension for all text documents produced using Microsoft Office Word. Given the open source nature of the XML specification, more alternative document processing applications support read and write capabilities on documents saved with the .docx filename extension. This is in comparison to the .doc filename extension which is a proprietary asset owned by Microsoft.
epub The ePub format is one of the many open source eBook file formats available. Initially released in 2007, it succeeded the legacy Open eBook format. The format was first defined by the Open eBook forum, part of the international digital publishing forum. EPUB digital books and publications all have the associated .epub extension and can be opened and viewed on any compatible device, software application, smartphone, or dedicated reader. The format is capable of optimizing the resolution of digital publications to suite the resolution of the device being used, making it inherently a 'reflowable' format.