Readwise Reader has a nice pdf reader with highlighting, notes, and an AI reader tool. I organize sources using tags. It's very new and in active development. A

Readwise Reader has a nice pdf reader with highlighting, notes, and an AI reader tool. I organize sources using tags. It's very new and in active development. Academic research is not it's main focus, though, so it probably won't add mindblowing academic tools. (like citation support/ backlinks. although it does have internet backlinks that tell you want articles link to the one you're reading)