my $CharSet = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'; # ASCII
my $BoldSet = '𝐚𝐛𝐜𝐝𝐞𝐟𝐠𝐡𝐢𝐣𝐤𝐥𝐦𝐧𝐨𝐩𝐪𝐫𝐬𝐭𝐮𝐯𝐰𝐱𝐲𝐳𝐀𝐁𝐂𝐃𝐄𝐅𝐆𝐇𝐈𝐉𝐊𝐋𝐌𝐍𝐎𝐏𝐐𝐑𝐒𝐓𝐔𝐕𝐖𝐗𝐘𝐙𝟎𝟏𝟐𝟑𝟒𝟓𝟔𝟕𝟖𝟗'; # UniCode bold

my $Source = 'The quick brown fox jumps over the lazy dog 1234567890 times.';
my $Target = $Source;
$Target =~ tr/$CharSet/$BoldSet/;

print "$Source\n$Target\n";

##</code><code>##

The quick brown fox jumps over the lazy dog 1234567890 times.
Toe quick bdown fox jumps oved toe llzy dog 1234567890 times.

##</code><code>##

This is perl 5, version 26, subversion 3 (v5.26.3) built for x86_64-linux-thread-multi
(with 51 registered patches, see perl -V for more detail)