Perusall is a social annotation tool that integrated into Classes. Perusall allows students and their instructors to collaboratively markup pdf documents. Instead of reading a document and discussing it, Perusall brings the discussion to the text.
Note: that if you used Perusall previously in Blackboard, you will have to check your email and approve that your are now switching your account to Brightspace.
For more information review the following tutorial from the section titled, Setting up your course: https://support.perusall.com/hc/en-us/articles/360033995014-Desire2Learn-Brightspace-setup