/usr/share/php/dompdf/dompdf_config.inc.php is in php-dompdf 0.6.2+dfsg-3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /etc/php-dompdf/dompdf_config.inc.php
/etc/php-dompdf/dompdf_config.inc.php