using System;

using System.Net;

using System.IO;

using System.Xml.Linq;

public class Program

{

    public static void Main()

    {

        string finalSvg = string.Empty;

        var webClient = new WebClient();

        byte[] imageBytes = webClient.DownloadData("https://cdn.shopify.com/s/files/1/0496/1029/files/Freesample.svg");

        var downloadStream = new StreamReader(webClient.OpenRead("https://cdn.shopify.com/s/files/1/0496/1029/files/Freesample.svg"));

​

​

        string rawSVG = string.Empty;

       //var ms = imageBytes..MediaStream.Stream;

       //var sr = new System.IO.StreamReader(downloadStream);

       rawSVG = downloadStream.ReadToEnd();

        //finalSvg = new MvcHtmlString(rawSVG).ToString();  

        AddAttribute(rawSVG);

        //Console.WriteLine(rawSVG);

    }

    public static void AddAttribute(string xmlData)

    {

        XDocument doc = XDocument.Parse(xmlData);   

        doc.Root.SetAttributeValue("class", "testclass");

        Console.WriteLine(doc.Root);            

    }

}