If I'm browsing your web application from my computer (which doesn't have a D: drive), how will my computer ever find "d:\Data\Issues\Ext Nos.pdf"? As far as my browser is concerned, it is looking for that file locally.
You'll need to build a page that takes the desired file name as a querystring argument (viewfile.aspx?file=d:\Data\Issues\Ext Nos.pdf) and reads that file and feeds back the binary data of that file. The only other option is to put the files in a disk location that is accessible thru your web server. Then you can provide the browser the web relative address to the file. For example:
1. Either put the files in a folder of the web application, or create a virtual directory that points to the server's physical location of those files:
Virtual directory in the root of the web server called "data" that points to "D:\data" on the web server.
2. Change your code to reflect the virtual location created in step 1:
frame1.Attributes("src") = "/data/Issues/Ext Nos.pdf"