Edit files using Office Compatibility Mode (OCM)
To open and edit Office files, you can use Office Compatibility Mode (OCM). With OCM, you can open and edit Office files in Drive, the Docs, Sheets, and Slides homescreens & apps, and Gmail.
On your mobile device, OCM is automatically included with the Docs, Sheets, and Slides apps.
When you open an Office file in one of the apps, you'll be able to edit it.
A bit of extra info:
Opening a Word document on Android just so you can read it is incredibly simple. Since Android natively supports opening .doc and .docx files, all you have to do is click on the file to open your Word document.
Find the file you want to open.
Tap to open the file – if prompted, open it in Google Drive or Google Docs if you have them installed already.
You’re now able to read the document.
To edit it, tap the small pencil icon in the bottom right – now you’ll be editing the file.
If you’d rather not use Google Drive or Google Docs, download Microsoft Office Word for Android and use that instead.