Ubuntu 16.04 does not come with php5 packages. However, Horde requires the PDO extension, which can be resolved by installing the php5.6-pgsql module. This fixes the Could not instantiate PDO. PDOException: could not find driver (1) error:

sudo apt-get install php5.6-pgsql

Incompatibility with PEAR's Services_Weather package

ParseError: syntax error, unexpected 'new' (T_NEW) in /usr/share/php/Services/Weather.php on line

Is 'resolved' by uninstalling the Services_Weather package as per Horde's mailing list comment:

sudo pear uninstall Services_Weather

According to the same thread,"pear package File_Fstab will also not work"src.

Install PHP SQLite extension

sudo apt-get install php7.0-sqlite;sudo service apache2 restart