A few weeks ago Google launched new Apps for Google Docs and Google Sheets. They have recently changed Google Drive App to a view only mode for Docs and Sheets. If you wish to edit your Docs or Sheets from a mobile device, you must download the new apps available for each type of document.
When you try to edit a document using Google Drive App, you will see a message like this:
You can click the message link within Google Drive App to download the free Apps or you can use one of these links:
Want more information about the Google Docs or Google Sheets Apps? Click HERE