To create a group:
Members of a group can copy records from a group folder and add them to their personal Zotero library. For more information on sharing libraries, check the Zotero Support page for Groups.
The Zotero plugin ZotFile helps you move your PDF highlights to notes in Zotero. The results can be a little messy, but depending on your learning style it might be a helpful way to gather your thoughts in one place, with the article citation. The resulting note file that is generated hyperlinks back to the text so you can easily get back to the original context.
There are a few steps to install this plugin, it is fairly well documented on the Zotfile website. Once installed:
This will generate a note with all of the highlighted text in it. This only works with PDFs that can be rendered as text, versus the older style of PDFs that are simply a picture of text. A good rule of thumb is if you can select, copy and paste text out of the PDF then Zotfile should be able to derive the text from your hightlights.