Web Forms :: Opening A PDF In An IFrame?

In a page I want to show a list box which will show all the PDF within a folder. Also besides that I want to show an Iframe or anything for that matter, in which I can show the PDF file content. The things that I tried are

1. Setting the src property of the IFRAME to the file clicked in Listbox

Problem :- It does only work for small PDF's. If the size of the PDF is large then this thing does not work, even waiting for a longer time PDF does not opens up

2. Using a code like this

string path = @"D:AmarCRM DocsCRM_SAP_Docs";
path = path + strParamFile;
System.Net.WebClient client = new System.Net.WebClient();
Byte[] buffer = client.DownloadData(path);
if (buffer != null)
{
Response.ContentType = "application/pdf";
Response.AddHeader("content-length", buffer.Length.ToString());
Response.BinaryWrite(buffer);
}

but with this approach the page is opened in the page & the Listbox for selecting the PDF file is not visible again.

So I did tried creating another page & setting the IFRAME src with the new page in which I can open up the file & again pass the control back to the first page. But somehow I am not able to do that.