Zotero 7 includes a document reader which helps you easily annotate PDFs or EPUBs. The annotations can then be extracted into notes and viewed from Zotero without opening the document again.
You can preview the attached document (PDF, EPUB) in Zotero's right-hand pane, after the Info section.
It is possible to extract all annotations made in PDFs as document notes.
To do this, right-click on the document, then choose Add note from annotations.
Here are few plugins (free add-on software) that you can download to add functionality to Zotero's PDF viewing and managing capabilities.
See more plugins here.