An Office Open XML Format file is actually a package of files and folders combined and compressed automatically using ZIP technology.
As mentioned in the preceding lesson, all Office Open XML Format files use ZIP compression technology. In fact, each Office Open XML Format file is actually a set of files compressed into what is known as a ZIP package.
If you change the file extension of any Office Open XML Format file to .zip, you can open that ZIP package in Windows Explorer to see all of the XML document parts, such as the top level of the ZIP package for a sample Word document, shown in the picture.
Note After you change the file extension of an Office Open XML Format document to .zip, the originating program (Word, Excel, or PowerPoint) will still recognize and open that file. However, for ease of use, it is always a good idea to change the file extension back to the original Office Open XML Format file extension once you have finished working with the ZIP package contents.