Convert Unix Epoch time to DateTime

EpochTimestampConverterToDateTime.cs

public static DateTime UnixTimestampToDateTime(string unixTimestamp)
{
    var time = Convert.ToDouble(unixTimestamp);
    DateTime dtDateTime = new DateTime(1970, 1, 1, 0, 0, 0, 0, System.DateTimeKind.Utc);
    dtDateTime = dtDateTime.AddSeconds(time).ToLocalTime();
    return dtDateTime;
}

EpochTimestampConverterToString.cs

public static string UnixTimeStampToString(string unixTimeStamp)
{
	var time = Convert.ToDouble(unixTimeStamp);
	DateTime dtDateTime = new DateTime(1970, 1, 1, 0, 0, 0, 0, System.DateTimeKind.Utc);
	dtDateTime = dtDateTime.AddSeconds(time).ToLocalTime();
	CultureInfo culture = new CultureInfo("en-US");
	return dtDateTime.ToString("d", DateTimeFormatInfo.InvariantInfo);
}