I assume it's a paper certificate and you want to print the class name and
your signature with your computer. I've done this and it's a pain in the
butt.
What I did was measure where the area where I wanted to add text. I started
with a blank document and did a lot of tweaking. Then I made copies of the
pre-printed cert and inserted them in the printer. I had to do a lot of
fudging to get it to the point where I was happy. (I know, I keep saying
that but that's because it's not something that you'll be able to do in 5
minutes. I want you to understand that you could spend a couple of hours
playing with this until you get it right. and then there's the cost involved
with the test prints.)
Are you really sure it's worth all of this? Don't your hard-working students
deserve something done by hand?