public static string ReplaceTokens(string template, Dictionary<string, string> replacements)
    {
        var rex = new Regex(@":{([^}]+)}”);
        return(rex.Replace(template, delegate(Match m)
        {
            string key = m.Groups[1].Value;
            string rep = replacements.ContainsKey(key)? replacements[key] : m.Value;
            return(rep);
        }));
    }

var saida = ReplaceTokens(stringDoArquivo, dicionarioValores);