C#: How do you determine the encoding of a file

Hi
I have a text file with words like "intimate°" intimateý & tête-à-tête There's probably others

Is there a way to work out its encoding?  I'm guessing extended ASCII  

I've been using code bellow or similar StreamReader / StreamWriter like I said this a pure guess  

string[] AllLines = File.ReadAllLines(FileName,Encoding.GetEncoding("iso-8859-1"));

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It looks OK on a sample file

Is there a Difference between StreamReader & File.Read..??

I'm assuming once you read a file into a string with a particular encoding the string inherits that encoding & this maintained if used in a class.