Here are some of the package versions that are installed:
ii apache2 2.4.25-3+deb9u6
ii davical 1.1.7-1~bpo9+1
ii dbconfig-pgsql 2.0.8
ii libapache2-mod-php 1:7.0+49
ii libapache2-mod-php7.0 7.0.30-0+deb9u1
ii openssl 1.1.0f-3+deb9u2
ii libssl1.1:amd64 1.1.0f-3+deb9u2
ii php 1:7.0+49
ii php-pgsql 1:7.0+49
ii php7.0 7.0.30-0+deb9u1
ii php7.0-pgsql 7.0.30-0+deb9u1
The pdo_pgsql module comes from package php7.0-pgsql:
# grep pdo_pgsql /var/lib/dpkg/info/*.list
/var/lib/dpkg/info/davical-doc.list:/usr/share/doc/davical-doc/api/function-check_pdo_pgsql.html
/var/lib/dpkg/info/davical-doc.list:/usr/share/doc/davical-doc/api/source-function-check_pdo_pgsql.html
/var/lib/dpkg/info/libphp-adodb.list:/usr/share/php/adodb/drivers/adodb-pdo_pgsql.inc.php
/var/lib/dpkg/info/php7.0-pgsql.list:/usr/lib/php/20151012/pdo_pgsql.so
/var/lib/dpkg/info/php7.0-pgsql.list:/usr/share/php7.0-pgsql/pgsql/pdo_pgsql.ini
