Here's how you can download and install the free Microsoft Office Mobile app for Office 365 on Android.
Download and Install Office Mobile for Office 365 for Android
1. Go to the Google Play page.
2. Tap the Install button.
Office Mobile for Office 365 on Android Official Description
"Please note: Office Mobile requires a qualifying Office 365 subscription. (See requirements below).
Microsoft Office Mobile is the official Office companion optimized for your Android phone. You can access, view and edit your Microsoft Word, Microsoft Excel and Microsoft PowerPoint documents from virtually anywhere. Documents look like the originals, thanks to support for charts, animations, SmartArt graphics and shapes. When you make quick edits or add comments to a document, the formatting and content remain intact."
Additional Resources for Office Mobile for Office 365 for Android