what namespace is required

private void button1_Click(object sender, EventArgs e)
       {
           IsApplictionInstalled(AcrobatReader);
       }
       public static bool IsApplictionInstalled(string p_name)
       {
           string displayName;
           RegistryKey key;
           // search in: CurrentUser
           key = Registry.CurrentUser.OpenSubKey(@"SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall");
           foreach (String keyName in key.GetSubKeyNames())
           {
               RegistryKey subkey = key.OpenSubKey(keyName);
               displayName = subkey.GetValue("DisplayName") as string;
               if (p_name.Equals(displayName, StringComparison.OrdinalIgnoreCase) == true)
               {
                   return true;
               }
           }