PHP should already have PDO extension enabled. What you probably need is the mysql driver for it.
# test if php5-mysql package is installed
dpkg-query --status php5-mysql | grep Status
# install the package if the above command indicates that it is not installed
sudo apt-get install php5-mysql
[Edit: oops, @ryanpq already answered]
You can do this with:
sudo apt-get update
sudo apt-get install pdo-mysql php5-mysql
If after this you are unable to use the extension you can check your /etc/php5/apache2/php.ini and make sure it includes:
extension=pdo.so
extension=pdo_mysql.so
/etc/php5/apache2/php.ini
in this path u mention, i dont have php5 folder. i have just php, in that php i have .git, 5.6, 7.0, 7.1, 7.2 folders like that.
after i did this.. " sudo apt-get install php5-mysql"
i got this...
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package php5-mysql is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source