There are two forms of Kami - an extension for Chrome/G Suite and a program/app. Either one, both are great and useful resource for solving PDF problems for free! They, of course coordinate and work together should you decide you need both. All in all, Kami is the exact tool you need for editing on a .PDF. Features include: highlighter, strikethrough and underline, add comments, text, paint features, shapes, and I'm really just getting started. I used this for school and currently use this for work, as well. After edits have been made, you can download as a PDF or upload to your Drive. I love it - it's really been a big help when working on PDFs.
As previously mentioned, it can be confusing at first - do you need or have the app or extension, but once you've sorted through this, it's great!