public class XMLHandler : IHttpHandler
{
    public void ProcessRequest(HttpContext ctx)
    {
        XmlTextReader reader = new XmlTextReader(ctx.Request.QueryString["document"]);
    ...
  }
}

public class XMLHandler : IHttpHandler
{
    public void ProcessRequest(HttpContext ctx)
    {
        // GOOD: use XmlReader
        XmlReader reader = XmlReader.create(ctx.Request.QueryString["document"]);
    ...
  }
}