Kami is an awesome online platform for annotating documents (Google files or pdf files). It also integrates well with Schoology to make the process of assigning and turning in documents easier.
This video offers a quick introduction to the website Kami, and how it can be used to annotate documents
The process of using Kami to annotate pdf files is made much easier when working with Kami. There is a small button (or text) within a Schoology assignment for your students to open the file in Kami, and once there, a small "Turn In" button appears it the top right corner to drive the file back to the assignment in Schoology.
In order for this to work:
Teacher needs to have the paid version of Kami and be using the Chrome browser
Students need the Kami extension installed in their Chrome browser (but do not need the paid version)
With the free version of Kami it is possible to connect Kami to your Google Drive account to pull in Google files such as Docs, Sheets, Slides, etc.
The paid version of Kami also allows you to import a variety of file types directly from your computer