FOP Editor is used to create PDF file from the input sources that are XSL:FO formatted. These input sources can be one of:
content of the FOP applet editor and data from HTML form
FO parameter - path to some FO file
XML+XSL parameters - paths to some XML and XSL files
PDF files are created using Apache Software Foundation's FOP tool. FOP is a Java application that reads a formatting object tree and then turns it into a PDF document. Submitting a input sources to FOP tool are accomplished through servlet. In this case, servlet is Enhydra application.