What does Autodesk’s .dwfx and Siemens UGS .jtx have in common? Both share OPC as a foundation. Open Packaging Conventions ("OPC") is a new file technology documented by the ISO/IEC 29500-2 and ECMA 376-2 standards.
System.IO.Packaging APIs were introduced with .NET 3.0 and Windows 7 include new native-code Win32 Packaging APIs.
More on the Microsoft Packaging Team Blog.