I’ve read many posts over the Internet which are stating that it is currently impossible to obfuscate WPF assemblies. Well this is partially true.

Here is what you can do to partially protect your .NET Framework 3.0 code:
In order your code to continue to work properly you must exclude from the obfuscation at least the names of your WPF window and user control classes. You can leave in the obfuscation the variables, methods, events, etc. declared in the codebehind unless you use some of them in your markup. If this is the case you must exclude those too.

Note that by doing this you will not obfuscate the XAML code itself, but only the codebehind. Your markup can still be viewed with some disassembly tools (for example Lutz Roeder’s .NET reflector and the BamlViewer add-in).