Folia is a great all-in-one solution, with a simple tool for marking up files with ink, a highlighter, or shapes and arrows. You need to create an account, but thankfully Folia lets you authenticate through Google (the way all Chromebook services should let you sign up).
You can import a file from your computer or many of the top cloud services—Dropbox, OneDrive, Box, and of course Google Drive are all supported.
The process to import your files takes a few too many clicks, but once it’s there you have a decent enough set of tools for marking up a file. You can then re-save them to your preferred cloud storage service for retrieval with email or other programs.