Google Drive for iOS can protect documents with a password, for that extra layer of security. Here is how you can add a password to a Google Drive document on your iPhone, iPad or iPod Touch.
To set this up, go to Settings.
From Settings, choose Password Lock. You will see the following screen.
Slide Password Lock to On. Now, you will be asked to enter the passcode for the device.
Enter the passcode. You will be asked to re-enter the passcode to confirm.
You will get to the Settings for Password Lock.
From this screen, you can disable Passcode Lock, change your passcode, or enable the passcode for the entire app, so that Google Drive asks for the passcode each time you open it.
You are all set!