Auto Populating Text-Fields

Okay, I asked a question similar to this but have done some testing and exploration with ideas. What I want to do is auto populate text fields between multiple PDF's in a portfolio; for example, if someone enters their name, I was going to use javascript to store the value in that text field as Applicant_first_name or something so that all other text fields that require the applicant's name will fill in the field with the variable value. Something like:

var applicant_first_name;

applicant_first_name = this.getField("Applicant_first_name").value;

This is terrible coding, but I'm new to javascript and the idea of implementing it into a pdf so I just need help to accomplish this. I've tried to find guides to accomplish simpler or related tasks but I had no success.