In previous versions of Office, to make a document read only, you need to right click, select properties and make the document read only. But Office 2007 has a built in feature inside word to make the document read only. The advantage of using the feature is that once the document is made read only, ribbon features are also disabled. To make a document read only, click on the office button on the top left corner and select Prepare. Inside prepare menu, you will be able to see the option, Mark as Final.
Once you select the option, you get a pop up confirming that the document will be saved and made read only.
Once the document is made final, you get a message that status property is set to final and typing and editing commands are turned off.
Now you can see that the ribbon features will be disabled and document cannot be edited, if you want to bring back the document to write mode, select Mark as Final option once again from the prepare menu.