You should look at 'Mendeley' which is primarily a Dropbox for the scientific Community. The Mendeley Desktop Application has Tabbedan integrated PDF-Viewer which supports PDF-Display and you can Highlitein Tabs, Text-Highlites and Notes. In the Screenshot you see two PDF's open in the Tabs and i have highlighted some Text at random to show.
The Desktop Software is free and you get 500 MB Space for sharing, like Dropbox you can expand that space with a premium (paid) Account.