What you want to do is automate the Internet Explorer UI. There are many libraries out there that will do this. You tell the library to find your window of interest, and then you can send keystrokes or commands to the window (CTRL-S in your case).
A good overview on how to do this in Perl is located here.
Example syntax:
my @keys = ( "%{F}", "{RIGHT}", "E", );
for my $key (@keys) {
SendKeys( $key, $pause_between_keypress );
}
The code starts with an array containing the keypresses. Note the format of the first three elements. The keypresses are: Alt+F, right arrow, and E. With the application open, this navigates the menu in order to open the editor.
Another option is to use LWP:
use LWP::Simple;
my $url = 'http://www.aeaweb.org/Annual_Meeting/pdfs/2014_Registration.pdf';
my $file = '2014_Registration.pdf';
getstore($url, $file);