After installing the plugin, you should run GitdenReader first and open PDF file
If you run this plugin alone, just a popup window appears and then the app is closed.
PDF Plugin for GitdenReader is based on the MuPDF library. It is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or any later version.
Source code available at https://github.com/gitden/pdf-plugin/