I need a mail merge done with over 1280 users.

I have a A4 letter with promotional text within it. We want it to be a personal letter with all the customer names included in it.

The A4 template has < and we have a spreadsheet full of names. So the job is to get the names of the spread sheet individually and then put them in the template and save it as a pdf with the name itself individually. All in all there is about 1280 customer. So we want a letter for all of them customer individually.