Office 2007 Documents Download As ZIP files

Problem

When attempting to download an Office 2007 file (.docx, .xlsx, etc) from a website in Internet Explorer, it downloads as zip file instead.

Fix

Often this problem arises from the actual web server not having the Office 2007 file format mime types registered. This should be addressed by the server admin.  If this is you (or you just want to be helpful to the server admin), then check out this TechNet article for guidance.

Although not recommended, you can also make a change in Internet Explorer that may address the issue.

1. Tools >> Internet Settings >> Security tab >> 
2. Select "Internet" zone
3. Click the "Custom level" button
4. Scroll down and change the setting for "Open files based  on content, not file type" to disabled.

Technical Resources

Office 2007 introduced XML based file formats for the new Office 2007 document types. Basically, an Office 2007 file is nothing but a zip file, with a different file extension, that contains various xml files where all the document data is stored. Office 2007 can open and interpret this data container structure so that a user will simply see an Office document.

Try it for yourself: Rename a file with a .docx extension to a .zip.  Then open the archive.

For more information about the new file formats, check out http://msdn.microsoft.com/en-us/library/aa338205.aspx.