Google Classroom is limited to users with an educational Google account, so you may have a hard time finding somebody who is both familiar with Google Classroom and the PDF world.
In general, when you display a PDF file in Google Chrome, by default, it will use it's own PDF viewer, which has a lot less capabilities than Adobe Acrobat or Adobe Reader. You can configure Chrome so that PDF files are opened in a standalone Acrobat or Adobe Reader application, but that may not work with the Google Classroom integration (again, I am not familiar, and I don't know how information is posted back to Google Classroom).
Acrobat and Reader used to work inside Chrome, but Google decided to pull the plug a while ago. This was not something that Adobe did, Chrome stopped supporting the kind of plug-in that Adobe provides. You can still use it for almost all other browsers, so the solution may be to stick with a browser that still allows you to open a PDF file inside the browser using Acrobat or Reader:
Karl Heinz Kremer
PDF Acrobatics Without a Net
PDF Software Development, Training and More...