The OneDrive mobile application for Android allows you to create a PDF copy of an Office document (Word, Excel or PowerPoint) and leverage the markup capabilities to highlight or make note to the document without changing the original one.
To start using it you need (of course) the OneDrive for Android mobile application (available here https://play.google.com/store/apps/details?id=com.microsoft.skydrive&hl=en_AU) configured to connect to your Office 365 account
Then open the OneDrive application and select the Office document you want to markup and click on the Markup (pen) button (the first time you will use it, a blue banner will show you the button)
Then confirm you are making a markup version and select the location where the copy will be saved
