split evaluates its argument in scalar context, so you only get one line. Splitting one line by two newlines doesn't make much sense. 
use strict;
use warnings;
use autodie;

open my $f, '<', 'data.txt';
my @words = split /\n\n+/, do { local $/; <$f> };
close $f;

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In reply to Re^3: regex question: store multiple lines as a string by moritz
in thread regex question: store multiple lines as a string by nurulnad

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