Microsoft yesterday released Office for Mobile Insider Build 16.0.14729.20000 for Android devices. This new update includes a new UI for PDFs using which you can access key PDF features from new bottom panel.
We’ve unveiled a new UI for PDFs in Office Mobile: a bottom panel that allows you to quickly discover key features. Now some of the most frequently used PDF features are visible at the bottom of the screen for easy access, including Edit, Bookmark, and Share. To access further options, just tap More.
Source: Microsoft