use strict;
use warnings;

open my $ifh, '>', 'test.txt' or die;
print $ifh "Hello world\n";
close $ifh;

system ('test.txt');
exit 0;
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"perl to generate files as outputs to test scripts ...(which) are sent all over the network depending on the board assembly and serial number."

I'm not quite clear about this: are the "test scripts" (perhaps non-Perl?) generating output that you're capturing with separate and distinct "perl" scripts and dispatching "all over the network" ... or are the test scripts written in perl (themselves) and using the board assembly and SN to determine where to send them?

Perhaps. OTOH, that's not important. In both cases, it sounds as though you could insert into your perl script a function to tee the output -- with one copy directed to notepad [scathing sarcasm about the juxtaposition of "notepad" and "appropriate" omitted :-)] or some other, more trustworthy text editor, and the other to the existing destination-selection function.

I don't know much about Perl on Windows, but fork and exec should work to pop open windows with those files.

Why not make Perl move the files to where they need to be on the network?

Both system(...) and exec(...) will work, but with openning up of the output file at the end of the perl script, I will favour exec(...) over system(...), because it exceute a system command and never returns to the original process.

check perldoc -f exec for more details