<?php
$data_final = '26/11/2017';
$ontem = DateTime::createFromFormat('d/m/Y', $data_final)->modify('-1 day');
echo $ontem->format('d/m/Y');
PD9waHAKCiRkYXRhX2ZpbmFsID0gJzI2LzExLzIwMTcnOwogICAgCiRvbnRlbSA9IERhdGVUaW1lOjpjcmVhdGVGcm9tRm9ybWF0KCdkL20vWScsICRkYXRhX2ZpbmFsKS0+bW9kaWZ5KCctMSBkYXknKTsKCmVjaG8gJG9udGVtLT5mb3JtYXQoJ2QvbS9ZJyk7