File Stream C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.Win32;
using System.Security;
class Utilities
{
    public static string GetContentType(string extension)
    {
        string mimeType = "application/unknown";
        try
        {
            RegistryKey regKey = Registry.ClassesRoot.OpenSubKey(extension, false);
            if (regKey != null && regKey.GetValue("Content Type") != null)
                mimeType = regKey.GetValue("Content Type").ToString();
            else
            {
                switch (extension)
                {
                    case ".xap":
                        mimeType = "application/x-silverlight-app";
                        break;
                }
            }
            return mimeType;
        }
        catch (SecurityException)
        {
        }
        switch (extension)
        {
            case ".docx":
            case ".doc":
                mimeType = "application/msword";
                break;
            case ".jpg":
            case ".jpeg":
                mimeType = "image/jpeg";
                break;
            case ".png":
                mimeType = "image/png";
                break;
        }
        return mimeType;
    }
}