Open XML is an open ECMA 376 standard and is also approved as ISO/IEC 29500 standard that defines a set of XML schemas for representing spreadsheets, charts, presentations, and word processing documents. Microsoft Office Word 2007, Excel 2007, and PowerPoint 2007 all use Open XML as default file format. Open XML file formats’re useful for developers because they use an open standard and are based on well-known technologies: ZIP and XML. Open XML SDK 2.0 for Microsoft Office is built on top of System.IO.Packaging API and provides strongly typed part classes to manipulate Open XML documents. SDK also uses .NET Framework Language-Integrated Query (LINQ) technology to provide strongly typed object access to XML content inside parts of Open XML documents.
More info: Download