Please take a look at the following link
https://groups.google.com/d/topic/pdfnet-sdk/DYh-MtpNWhc/discussion
Basically, the add-on features including the annotation handling are implemented in Tools.jar. Licensed customers are given the source code of Tools.jar for full customization and rapid development.
Update: Starting with version 6.1.0 of the Android PDFNet SDK, the Tools library is now shipped as an Android Library, and its source code can be found in the samples folder. The package does not include the Tools.jar anymore, and you now have the flexibility to include the source directly into your project or create a separate library for your projects.