Thank you for the advice; something I will keep in mind when setting up signatures.
Several days ago I stumbled on a solution. Turns out the last line of certificate.php was:
certificate_print_text($pdf, $custx, $custy, 'L', '', '', '', $certificate->customtext);
When I looked at a newer version I was testing it read (Note the difference in parameters shownin red):
certificate_print_text($pdf, $custx, $custy, 'L', null, null, null, $certificate->customtext);
Since I can't update the entire module I changed the line to read like the newer version and it worked. Hope this helps others who may be experiencing this.