The 2007 Microsoft Office system introduces a new file format that is based on XML called Open XML Formats. Microsoft Office Word 2007, Microsoft Office Excel 2007, and Microsoft Office PowerPoint 2007 all use these formats as the default file format.
Open XML formats are useful for developers because they are an open standard and are based on well-known technologies: ZIP and XML. Microsoft provides a library for accessing these files as part of the WinFX technologies in the System.IO.Packaging namespace.
The Open XML Format SDK is built on top of the System.IO.Packaging API and provides strongly typed part classes to manipulate Open XML documents.