[c#] How to open PDF file in a new tab or window instead of downloading it (using asp.net)?

This is the code for downloading the file.

System.IO.FileStream fs = new System.IO.FileStream(Path+"\\"+fileName, System.IO.FileMode.Open, System.IO.FileAccess.Read);
byte[] ar = new byte[(int)fs.Length];
fs.Read(ar, 0, (int)fs.Length);
fs.Close();

Response.AddHeader("content-disposition", "attachment;filename=" + AccNo+".pdf");
Response.ContentType = "application/octectstream";
Response.BinaryWrite(ar);
Response.End();

When this code is executed, it will ask user to open or save the file. Instead of this I need to open a new tab or window and display the file. How can I achieve this?

NOTE:

File won't necessary be located in the website folder. It might be located in an other folder.

Instead of loading a stream into a byte array and writing it to the response stream, you should have a look at HttpResponse.TransmitFile

Response.ContentType = "Application/pdf";
Response.TransmitFile(pathtofile);

If you want the PDF to open in a new window you would have to open the downloading page in a new window, for example like this:

<a href="viewpdf.aspx" target="_blank">View PDF</a>