Why Format section gets disabled when we create Merge Template over PDF

Why Format section gets disabled when we create Merge Template over PDF

I need some assistance I have a Client who is going to give certificates to users who passes his exam. So, I am using mail merge but in ZOHO writer after I upload the PDF and create merge Template over PDF the format Section gets disabled.

My problem is I am gonna add the Student Name etc. on certificate and data in the field does not get center aligned, I think it is maybe due to format section getting disable somehow.
And I cant get my work done like this because Certificate doesn't look professional at all. Name and everything else added on the certificate doesn't look proper.

I'll appreciate any help.