Response.TransmitFile is not opening the links directly from SharePoint Library c#

Hi,

 I want to open a pdf file from a sharepoint library. I am using Response.TransmitFile to do that. But it throws me the error "'url' is not a valid virtual path". Is there anyway otherway to do this.

            Response.Clear();
            Response.ClearHeaders();            
            Response.ContentType = "application/pdf";
            Response.TransmitFile("URL to the library" + fileName);
            Response.Flush();
            Response.End();