Reading dnd4e Files into a C# Program?

I’m writing a program that I want to have be capable of using the files generated by the Character Builder WotC put out. Problem is, I have no idea how to load the files into my program. I know that they’re just xml files with a different extension, but even if they had the standard xml extension I’m not sure how to begin coding to load in the file so I can let my users use their character sheets with my program. I also want to be able to let users save their files as dnd4e files. Does anyone have any clues how to code this?