I have alot of knowledge on parsing office file format what are you trying to do exactly? There is also as pose but that's a paid solution.
What I don't understand is how are multiple layers implemented in OneNote? How can one add SVG based drawings/annotations on typed text and move those annotations around. How is this encoded in the format, which seems pretty complex just thinking about it initially at least. My thinking was that if I could see a onenote parser, I could play around with a one-note document to see how it works? If that's not possible, I was wondering if there is any other open source format in which we annotate typed texts with hand drawing like in OneNote and how is that handled?