Robin Good: PDF Presenter is an open-source free cross-platform presentation software which allows you to edit and annotate existing content, import images and draw annotations .
With PDF Presenter you can type text next or over existing content, create multiple tabs with different whiteboards, and save your final work as a PDF file.
Java version 6 or higher.
Works on PC, Mac and Linux.
Free to use.
More info and download it here: http://pdfpresenter.sourceforge.net/
(Thanks to Baiba Svenca for uncovering it)