Bookmarks won't work if your script is using a UNC path. Read the note here:
http://kb2.adobe.com/cps/317/317300.htmlYou have to set a destination for it to work with UNC paths. Also, you would have to change the header to automatically open the file instead of prompting for open/save:
Change:
header("Content-Disposition: attachment; filename=\"$asfname\"");
To this:
header("Content-Disposition: filename=\"$asfname\"");
I tried it out and it worked fine for me. A bookmark anchor did not work, but adding a destination did. The file would be called like download.php?f=filename.pdf#destinationname