I don'n run my wiki as a local program, so I have to guess how it may work ...
Did you try
http://127.0.0.1/dokuwiki/data/media/docpdf/essaipdf.pdf
or
http://localhost/dokuwiki/data/media/docpdf/essaipdf.pdf
Probably the file can be opened with a link to your drive and directory.
For example:
<html>
<object data="c:\dokuwiki\data\media\docpdf\essaipdf.pdf" type="application/pdf" width=800 height=500></object>
</html>
if drive "C" is the one where DokuWiki is installed in "c:\dokuwiki" (that's the way you open any local file with a browser).
What about this versions:
/home/user/htdocs/dokuwiki/data/media/docpdf/essaipdf.pdf
or just
localhost/dokuwiki/data/media/docpdf/essaipdf.pdf
Good luck ;-)
Wolfgang