Google Drive api scope and file access (drive vs drive.files)

The difference is that 'drive.file' only gives you permission to files that your app has created or the user has explicitly shared with your app, whereas 'drive' gives your app permission to see the all the files in the user's drive.

See

https://developers.google.com/drive/web/scopes

You should really look into using drive.file, that is where they are trying to push users. I was just fighting with this myself and found that if you use the drive.file scope, you can then subsequently open the file that is chosen using the API for the file type, but only if you set the correct AppID.

See here: https://developers.google.com/picker/docs/#gdata

This allows you to get past the 404 error that you get if you don't set the AppID.