Import data from Excel (text file) into fillable PDF form to create multiple documents

What you are asking about is called a variable data process, also called a mail merge. 

There is no built-in feature for this in Acrobat, but there are ways to do it. People have written Acroat automation scripts for this (try67 has one)

 Custom-made Adobe Scripts: Acrobat -- Mail Merge and Email PDF Files

and there are plug-ins (such as the one from EverMap). I've written my share of data import scripts tools, but don't yet have a mail merge tool.

https://www.pdfscripting.com/public/Form-Data-Handling.cfm

You'll find other answers as well by searching for "Mail Merge" on this forum.