In Google drive app, you can download a copy for offline. Start Google Drive app. tap and hold the file until the option box pops out. You can choose Download a copy.
For file manager, Motorola does not ship it because there are so many good apps in the Play store. My recommendation is ES File Explorer (you may check this guide on basic usage of ES File explorer: http://motoeguide.com/moto-e-guides/manage-files-moto-e-es-file-explorer-file-manager/ )