Way to get absolute path of file PHP
__FILE__
That is the absolute path to the file being executed.
simple usage examples:
echo __FILE__;
echo "This file is: " . __FILE__;
You can try like this
include dirname(__FILE__).'/../yourfile.php';
Since PHP 5.3.0 you can use also the magic constant __DIR__
More info in the docs
Another way is
$rootDir = realpath($_SERVER["DOCUMENT_ROOT"]);
include "$rootDir/yourfile.php";