In case it should turn out that Word can't encode the XML itself, you could use

use HTML::Entities qw(encode_entities_numeric);

# unicode/character string
my $in = qq(Sample data & and text for some <conversion> \x{201C}text\
+x{201D}.);  

print encode_entities_numeric($in);
    
__END__
Sample data &#x26; and text for some &#x3C;conversion&#x3E; &#x201C;te
+xt&#x201D;.
[download]

(that is, if you can get away without the (IMHO superfluous) leading zeros in the hex values...)