The right pane on Mendeley Desktop is where you'll find document details.
Clicking on the Notes tab at the top, allows you to add notes and see a record of .pdf annotations.
Mendeley allows you to work with .pdf files directly in your Mendeley Desktop library.
Double click on a .pdf document in your list of references, and the document will open in the center pane. The right pane will continue to show document details.
The toolbar of the .pdf viewer allows you to:
You can share this document with others in private groups. Each person's annotations will be in different colors.
A .pdf will open in Mendeley at the last page viewed, so that you can continue working where you left off.