If a PDF is attached to a reference you can use the annotation feature to highlight and add comments. Simply double-click the citation that you would like to annotate.
You can also add notes to a reference. To do this click on the reference and select Notebook from the tabs on the window that opens on the right.

Annotation View
Within the annotation view you can:
- highlight text in multiple colors
- add comments
- zoom in and out
- download the annotated PDF
