FileDefinition is useful to attach resources to your process definition. Any file other than processdefinition.xml that you include in your process archive can be retrieved using its path within the archive:

FileDefinition fileDefinition = processDefinition.getFileDefinition();
InputStream goodiesStream = fileDefinition.getInputStream("path/to/goodies.properties");
byte[] goodiesRawBytes = fileDefinition.getBytes("path/to/goodies.properties");

Normally your files are saved in the database. If your database has problems with large binary data, you can tell jBPM to store your files in the filesystem by setting the property "jbpm.files.dir" in your jbpm.properties to an absolute local path.

For a practical example, see: http://www.jboss.org/index.html?module=bb&op=viewtopic&t=67818