I saw this question asked internally today, so I thought I would share. If you want to develop to use the Open XML document format you probably want to look at two things. The Microsoft resources (eg http://msdn2.microsoft.com/en-gb/office/aa905545.aspx ) and the ECMA resources Standard ECMA-376 . On the MSDN site you will find documentation and a MS SDK (less interest if you are developing using a functional language for your mainframe ). The ECMA site has the following: Standard ECMA-376 Office Open XML File Formats (December 2006) This Standard defines Office Open XML's vocabularies and document representation and packaging. It also specifies requirements for consumers and producers of Office Open XML. An Office Open XML overview is available on the Ecma website. Copy these file(s), free of charge: File name Size (Bytes) Content ECMA-376 Part 1 350 630 zipped DOCX file ECMA-376 Part 1 1 441 795 zipped PDF file ECMA-376 Part 2 341 625 zipped DOCX file with 2 Annexes ECMA-376 Part 2 1 286 494 zipped PDF file...