What's a good Android app for quickly reviewing and annotating research papers while I'm commuting?

For academics who are constantly on the move, the Android version of Microsoft Word presents a surprisingly elegant solution for reviewing documents. I've found it particularly useful for quickly annotating research papers during my commute. The cross-platform compatibility is key; I can start editing on my desktop and seamlessly continue on my phone. The annotation tools, while not as extensive as the desktop version, are more than adequate for adding comments and highlighting key sections. It's also helpful for managing citations, as it integrates reasonably well with reference management software. This novel approach to an old problem—document editing—makes it an intellectually satisfying tool for any researcher.