Draw on pdf
Chrome has this feature, and online solutions (like pdfescape) do so too,
this is particularly useful to highlight parts of a tab (let's say I want to highlight 3 rows but want the reader to focus on 1 in particular, I can simply circle it in red).
It would be nice having shapes (squares/circles) and freestyle, so one can draw (with mouse or tablet).
Colors and thickness could be adjustable.
This is a feature to improve note taking, however I didn't want to include it in #1134 as I thought it would get lost there and a separated ticket would be better.