This should do it:
Encoding wind1252 = Encoding.GetEncoding(1252);
Encoding utf8 = Encoding.UTF8;
byte[] wind1252Bytes = wind1252.GetBytes(strHtml);
byte[] utf8Bytes = Encoding.Convert(wind1252, utf8, wind1252Bytes);
string utf8String = Encoding.UTF8.GetString(utf8Bytes);