opening pdf file

Hi
 I have asp.net page     I am using   file upload     to put files in server      so  it's work great

and I have another page  to view  this files   usually  I am using   .pdf  file    for this  my  way   is  using   hyper link     (ip address/folder name/ file name.pdf)
and  it's working  great  to view files     but there is big problem there is no security    means     user can take  path of file      close  system 
and paste it in URL unfortunately file opened 

How can I solve this problem      opening  files  in asp page     or what

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