“Zotero 6 introduces an array of new features to transform how you do research, including a completely new way of working with PDFs and notes.”
A free, open source reference manager now ships its own PDF reader, with annotations that sync across devices and shared group libraries. Highlight on an iPad and pull the quote straight into your paper on the desktop. Researchers pay for commercial tools that do less. Free software that respects your library beats them on features.