how to open PDF at runtime using XSLFO input

   I have the following code that creates the PDF file on the machine. But, I require, I user click on the View PDF link, the PDF file should be generated at runtime and open.

string inputString = "PGZvOnJvb3QgeG1sbnM6Zm89Imh0dHA6Ly93==";
//parameters for the rendering operation.
RenderingParameters param = new RenderingParameters();
//set input format
param.InputFormat = Engine.InputFormat.XSLFO;
//set output format
param.OutputFormat = Engine.OutputFormat.PDF;

Engine engine = new Engine();
System.Text.UTF8Encoding encoding = new System.Text.UTF8Encoding();
byte[] stringBytes = Convert.FromBase64String(inputString);
//create input and output streams
Stream inputStream = new MemoryStream(stringBytes);

//create input and output streams
using (FileStream outputStream = new FileStream("C:\\HelloWorld1.pdf", FileMode.Create))
{
    engine.Render(inputStream, outputStream, param);
}

How can I write code to open the PDF on the fly without writing on the disk?