The solution you have posted is somewhat clunky - in that it does not read like "normal" perl.

Here is a tested, more perlish alternative:

use strict;
use warnings;
use Win32::OLE qw(in); # "in" provides the enumeration mechanism#

use Win32::OLE::Const 'Microsoft Word';

my $file = 'C:\Users\Netwallah\My Documents\test.docx';

my $WordApp = Win32::OLE->new('Word.Application', 'Quit');
#$WordApp->{'Visible'} = 0;
my $doc = $WordApp->Documents->Open($file) or
    die("Unable to open document '$file':", Win32::OLE->LastError());
for my $para (in $doc->Paragraphs()){
    for my $CurrentWord (in $para->{Range}->Words()){
       next unless $CurrentWord->Text() =~/perl/i;
       $CurrentWord->Font->{Bold} = 1;
    }
}
$doc->Save();
$WordApp->ActiveDocument->Close ;
$WordApp->Quit;
[download]