This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
It would be helpful to have a frame of reference, like where you heard or read those terms. I'd say an application class is one that has a main method or extends Applet, or in some other way runs your application. I'd put thread classes in this group also. An object class is one that models a real world object, idea (like a data structure), or abstraction. The vast majority of classes you write will be object classes.
I’ve looked at a lot of different solutions, and in my humble opinion Aspose is the way to go. Here’s the link: http://aspose.com