Thanks, Dan. Your suggestion should work on most cases like this. But, my problem is, all my links are in PDF file and I have no way to make changes in those links. The good news is, all links are calling a same logging page and then redirected to the destination page. The logging page is written in ASP. I am thinking to add some codes on this page so it will only open window once. Do you have any idea how to do that?
Thanks a lot!