I did change the path as you said.
require_once '/var/www/html/site/core/components/docmanager/model/docmanager/docmanager.class.php';
But now I’m getting this error.
(ERROR @ /var/www/html/site/core/xpdo/xpdo.class.php : 503) Path specified for package docmanager is not a valid or accessible directory: indexmodel/
I change the path too for the next lines but I’m getting the same error mentioned above.