It's gonna be a b*tch. You are going to have to do some measuring and
tweaking, etc.

It will be much easier if you fill in the blanks by hand. If your
handwriting is anything like mine, you'll have to take your time and do it
neat.

Mail merge. Just scan the certificate in, shove it in the background,
lay out your merge fields so they are spot on the lines supplied, then
delete the background and Print > Merge. Simple.