Doesn't the following work?

$content =~ s/&/&/g;
$content =~ s/</&lt;/g;
$content =~ s/>/&gt;/g;  # optional.
print("<textarea>$content</textarea>");
[download]

To save it:

open(FILE, "> file.html");
print FILE $cgi->param('content');
close(FILE);
[download]