There are any number of XML APIs you could use: SAX, DOM, XPath, dom4j, XOM, JDOM, StAX... If you haven't used any API, try out a few to see which you like best.
I probably wouldn't start with SAX, though, it requires more code to be written than most of the other APIs. XPath might be a good fit if you want to extract a few specific, well-defined values out of a document.
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