Files with the ZFO extension are most commonly used by the 602XML Filler e-form filler. ZFO files are files that allow for proper formatting of forms created in XML format. ZFO files are created in XSL-FO format, which is also a simple programming language. These files are used to give the correct layout, font formatting and colors of XML documents. In this sense, they perform a similar function to CSS files for HTML documents.

602XML Filler is a free tool developed by Software602, Inc.