Ubuntu – Connection failed to open the DB connection: could not find driver

At this stage I would simply recommend "turning it off and on again" by doing:

sudo apt-get purge php-common php5-common

followed by

sudo rm -r /etc/php

And then reinstalling PHP 7.0 and mysql modules:

sudo apt-get install libapache2-mod-php php-mysql

You may also try just purging and reinstalling mysql modules, first removing the package:

sudo apt-get purge php7.0-mysql

And the installing them again:

sudo apt-get install php-mysql

In both cases it's important to use apt-get purge instead of apt-get remove to delete any existing configuration files and package states.

The least destructive way would be trying to re-enable mysql modules using phpenmod command:

sudo phpenmod mysqlnd pdo_mysql

It's hard to give you correct advice if we don't know what mayhem you created on your system.

Dynamic link libraries (DLLs) are a Windows-specific technology and don't work on Ubuntu. Because PHP can be run on different operating systems, its configuration files contain examples for how to configure it on different operating systems:

;;;;;;;;;;;;;;;;;;;;;;
; Dynamic Extensions ;
;;;;;;;;;;;;;;;;;;;;;;

; If you wish to have an extension loaded automatically, use the following
; syntax:
;
;   extension=modulename.extension
;
; For example, on Windows:
;
;   extension=msql.dll
;
; ... or under UNIX:
;
;   extension=msql.so
;
; ... or with a path:
;
;   extension=/path/to/extension/msql.so

Normally, the Linux build of PHP already comes with SSL support built in, in contrast to the Windows build, where you need the DLL you mentioned. But you seem to use a third-party build of PHP 7 (maybe a from PPA?), because Ubuntu 14.04 comes with PHP 5 by default. So this third-party build might handle SSL differently.