using System;

public class Program

{

    /*

      private string GetTruncatedDisplayString(string param)

      {

         if (!param.Contains("."))

            return param;

         var parts = param.Split('.');

         if (parts[1].Length <= 7) 

            return param;

         double number;

         if (double.TryParse(param, out number) == false)

            return param;

         double roundValue = number.RoundToSignificantFigures(7);

         return roundValue.ToString();

      }

      */

    private static string RoundToDecimalPoints(string param, int places = 7)

    {

        if (string.IsNullOrWhiteSpace(param))

            return param;

        if (!double.TryParse(param, out double number))

            return param;

        try

        {

            return (number * Math.Pow(10, places) == Math.Floor(number * Math.Pow(10, places)))

                ? param

                : number.ToString($"F{places}");

        }

        catch { return param; }

      }

    public static void Main()

    {

        foreach (var testString in new[] { "notAString", null, string.Empty, "5", "7.1", "07.12", "7.123456", "00.1234567890", "0.0000001" })

        {

            Console.WriteLine($"value={testString} | RoundToDecimalPoints(value)={RoundToDecimalPoints(testString)}");

        }

    }

}