This plugin integrates power of Google doc pdf viewer with your application, though this plugin has been created using Grails-1.3.4 but it supports all version from Grails-1.1.
Example - Whenever pdf is attached as attachment to gmail , it gives two options 1) download 2) View When user selects view is opens pdf in GoogleDoc, similar functionality is provided by this plugin. You simply need to provide full path to tag provided by taglib.
<pdf:isSupportedByGoogleDocs params="['fullPath':fullPath,chrome:true]"> View on Google Docs </pdf:isSupportedByGoogleDocs>
IMPORTANT: Action viewPdf of controller PdfViewer must be public, so that google can access it.