PDF notes have been removed in favor of using web links.
More detail: It was very difficult to find a version of PDF notes that worked in all PDF viewers in a consistent way. What we wanted to do was have an icon show up that you could hover over or click on that would provide more information. But some viewers showed the information, some didn't, and overall it was a mess. So we opted to just put an icon in the margin that you can click on and it will take you to a relevant web page (on the FBS wiki or elsewhere).