Romat, H., Pietriga, E., Riche, N. H., Hinckley, K., & Appert, C. (2019, October 1). SpaceInk: Making Space for In-Context Annotations. UIST 2019 32nd ACM User Interface Software and Technology Symposium.

https://www.microsoft.com/en-us/research/publication/spaceink-making-space-for-in-context-annotations/

https://www.youtube.com/watch?v=fbPD5_wPapQ

Lovely design from Microsoft Research for making more space inline for annotations / notes within a PDF.

Related; Few digital reading environments support marginal notes