.NET Reflector: item is obfuscated and can not be translated

Hi all,
I need to see and debug the code in a Dll which I don't have the source code.
But when I use .NET Reflector I'm having several of this messages:

protected void fillddlGroup()
       
{
            // This item is obfuscated and can not be translated.
       
}

private string g()
       
{
           
// This item is obfuscated and can not be translated.
       
}

Why this happens, and how can I see the original code?

Thanks in advance.

Luis