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.
Updates are gradually rolled out, so you may not be able to install the latest version of the Google Drive app from Google Play. Android Police has a link to the APK file.