References within the ReadCube Papers Web Reader have several annotation features available.
The first are highlights, which are available in 4 different colors. To highlight, just select the desired text and a menu will pop up. Choose the appropriate color and your text will immediately be highlighted.
To delete unwanted highlights, select an existing annotation and choose the delete option on the bottom left of the web reader
Following the same procedure as explained above, you can also add notes. All of these notes and highlights can be viewed from the upper left-side menu by selecting the "Notes" tab.