php - How to Prevent Copying PDF to Another Computer -

i bought book on leanpub.com. interested in technique can copy flashdisk, file can not opened on computer (i seen white screen).
every person sells @ leanpub upload files have been protected or leanpub.com create protected file @ runtime when people execute link?
if created in runtime, how do php?

edit 1
in simple word; want create system protect pdf file in website leanpub. so, people have download file, can't copy others.

edit 2
why people down vote? don't think oot. interesting leanpub technique protect publisher right. care user right...
have been searching http://php.net/manual/en/book.pdf.php. can't solve it.

    header("content-disposition: attachment; filename=".urlencode($the_file);        header("content-type: application/force-download");     header("content-type: application/octet-stream");     header("content-type: application/download");     header("content-description: file transfer");                 header("content-length: ".filesize($the_file));     //is possible solution here add more header protect publisher right??     flush();      $fp = fopen($file, "r");     while (!feof($fp))     {         echo fread($fp, 65536);         flush(); // essential large downloads     }      fclose($fp); 

above code add more header current pdf file sending url , force browser download.
there possible solution add more header current pdf?

you use truecrypt encrypt flashdrive. way, nobody able hands on contents of drive without passphrase.

or use 7-zip password protect .zip file has .pdf in it. way, need password in order file.

i hope helps!