Drupal Fatal error Class 'PDO' not found in Drupal/Core/Database/Driver/mysql/Connection.php

 Below a steps required to fix the above issue.

Step 1-  Enable PDO in your php.ini file 

Step 2-  open php.ini file add below line

extension=pdo.so

extension=pdo_sqlite.so

extension=pdo_mysql.so

extension=sqlite.so

Once you made this change kindly restart your DB Server. After that you refresh your website.