XML editor

Question

I need to show the entire content of an xml file. I've done it with File.ReadAllText("name.xml") and put the content in a textbox. But i need instead of a simple textbox smth like notepad++ ..i'm reading very big xml files..so i need that +/- option to view more/less text. I need a hint..where can i find such open source? And how it's best to read a xml file? Thx