There is only one file type that uses the .XFO extension:
XSL-FO Formatted Form
Form that is formatted using on the XSL-FO (Extensible Stylesheet Language - Formatting Objects) markup language; defines how XML data is formatted for the screen, print, or other type of media; may be used in online or offline applications.
XSL-FO Forms more commonly use the .FO extension.
Updated: November 21, 2007