If you want to see the application code, you need to look into your strut-config.xml file
Look at my example : you see the .do is define there as the path of your web application. The browser will show that in the url box. If you want to see the code, you must look into your action file : com.search.SearchAction.java. When you call a webpage inside your application, you will use the forward name, so the webapplication will know which action to use and which method inside the action to call.
If you don't have the application code, you can't see what is in .do file. It's not some type of archive like you seem to think it is.