Download File from ListItem

public void DownloadAttachedFileFromListItem

( 

string siteUrl,  

string webName,  

int itemId,  

string attachmentName,  

string listName,  

string downloadLocation

)
{
    using (ClientContext clientContext = new ClientContext(siteUrl))
    {
        string attachmentPath = string.Format("/{0}/lists/{1}/Attachments/{2}/{3}", 

webName, listName, itemId, Path.GetFileName(attachmentName));
        var fileInformation = File.OpenBinaryDirect(clientContext, attachmentPath);
        IList<byte> content = new List<byte>();
        int b;
        while ((b = fileInformation.Stream.ReadByte()) != -1)
        {
            content.Add((byte)b);
        }
        var downloadFileName = Path.Combine(downloadLocation, attachmentName);
        System.IO.File.WriteAllBytes(downloadFileName, content.ToArray());
        fileInformation.Stream.Close();
    }
}