Restrict the User to open the Page in web application

Question

Hi Friends,

i have a client requirement in my Online Test Application Project, that user who logins and currently goin through his test process

should not be able to open the file again in another Web Browser.

my flow is like dis, i have a gridview in which i have a pdf file hyperlink for the user learning, then on clicking the checkbox besides the pdf file link the assessment page opens up and user gives his answers and all....but i have to restrict the user that he should not go through another browser and opens up the same pdf file page in another window, it should be disable at that time...untill the test which is goin in previous web browser gets completed.

how can i able to restrict the user!

pls do post ur answers.

Regards,

Aamir