Hi cisman,
try
rename($filename, "$pdc_root/" .$filename_name);
and make sure that $pdc_root/ is totaly qualified (i had some problems when i used it in the way: $pdc_root/ = "../dir1/", use eg. "/var/www/dir1/" instead that works always... and of course the 'input type="file"' needs the name="filename" (just in case you forgotten...)
cya Rob