When you edit or open your Dropbox files with a third-party application, you have the choice to set that app as the default for opening files of that type. To set a default app to open certain file types: Tap on the file you'd like to open/edit to preview it. Once the document preview loads, tap the Edit icon (it looks like a pencil and paper). You will see a list of available third-party apps. Tap the app you'd like to use to open your file. You'll have the option to use this app Always or Just once. Choosing Always sets this app as the default app for opening this file-type from Dropbox. If you ever want to change or clear your default apps, you can do so from the Dropbox settings: Open the Dropbox app. Tap the menu button. Select Settings. Scroll down and tap Manage default apps. Find the app you'd like to remove and tap Remove. Confirm the removal by tapping Clear.