The SDK is built on the System.IO.Packaging API and provides strongly-typed classes to manipulate documents that adhere to the Office Open XML File Formats Specification. The Office Open XML File Formats specification is an open, international,ECMA-376, Second Edition and ISO/IEC 29500 standard. The Open XML file formats are useful for developers because they are an open standard and are based on well-known technologies: ZIP and XML.
The Open XML SDK 2.5 simplifies the task of manipulating Open XML packages and the underlying Open XML schema elements within a package. The Open XML SDK 2.5 encapsulates many common tasks that developers perform on Open XML packages, so that you can perform complex operations with just a few lines of code.