Well if you are talking about a "Google Drive" account, it depends on if you are trying to view them through the app or not. If you are... You can't just 'view' and open them that way. You can, however, view a list of the files and select those you wish to download back to your phone.
To just view them, without downloading, you would have to do it from a computer.
To download a file, using the app, which will allow you to see a list of files/names....
1. Tap and open the Google Drive app.
2. Tap, and then hold, each file you’d like to select to download.
3. Then tap Download.