The latest version of Google Drive for Android added a lot of new features: a new interface based on Material Design, a better search feature that shows results as you type, custom message for sharing files. "You can also turn on link sharing to make the file public and set access to view, comment, or edit. This automatically copies the link to the clipboard and allows you to paste it wherever you want."
Google Drive for Android now also includes a PDF reader. The application still uses the default PDF reader installed on your device, but you can now select Drive PDF Viewer. It works offline and it can be used from any other Android application, not just from Google Drive.
Google's PDF viewer is pretty basic: it has a search feature, it lets you select and copy text, upload files to Google Drive, print files and share them.