This plugin contains code from the pixie project (http://www.jfree.org/download/) licensed under LGPL v 2.1. A copy of which is included as part of this jar file. 

You can download the source code for the version that Atlassian uses here:

https://maven.atlassian.com/public/com/atlassian/confluence/officeconnector/pixie/1.3.7/pixie-1.3.7-sources.jar