A better fix would be to consider all possible Html Entities like this:
private const string HtmlEntitiesPattern = @"&([a-z]{2,10}|#\d{1,10}|#x[0-9a-f]{1,8});";
private static readonly Regex HtmlEntitiesPatternRegex = new Regex(HtmlEntitiesPattern, RegexOptions.Compiled | RegexOptions.IgnoreCase);
public static string FixDoublEntityEncoding(string document)
{
return HtmlEntitiesPatternRegex.Replace(document, "&$1;");
}