- Sign in to dropbox.com.
- Preview a Word, Excel, or PowerPoint file that's saved in a shared folder.
- Click the arrow next to the Open button.
- Select Microsoft [Excel/PowerPoint/Word] Online.
- Sign in with your Office 365 credentials if prompted. (Note: Your Office 365 account must have a subscription that includes the Office Online products.)
- The file will open in your web browser in Office Online, where you can edit it.
- When you're done editing, click Save and return to Dropbox.
- At the top of the page you can see your name, and the names of other people who have the same file open.
- Changes you make will be saved automatically to your Dropbox.