The short and sweet of it..
Version 4 can be downloaded below. To use just start annotating on the whiteboard and save to location. If you want to add a .pdf document just drag and drop it onto the page. Give it a few seconds to load (there is no progress bar or beach ball indicator I am aware) and the pdf will be imported. Use the buttons in the corner to remove pdf documents and add in another. They will overlap! Be sure to clear documents before adding in another. I will raycast the documents so in future you could have a massive “mind map” of relevant documents to share with students.
This is a personal project, I will release open source when I can polish it more. I dont have time. Feel free to spread the word if you find it useful to motivate me to finish it at somepoint.
Check out the following links for inspiration and further reading about this topic