XFA stands for XML Forms Architecture, and is part of a family of proprietary XML specifications that were developed by JetForm to enhance the processing of web based forms, however starting at PDF Specfication 1.5 it was possible to be used with XFA, but XML Forms Architecture was not standardized when the PDF Format became an ISO standard.
XFA
What is PDF.js? PDF.js is an open-source (licensed under Apache 2.0) JavaScript library developed by Mozilla that enables the rendering of Portable Document Format... What are HTML forms? HTML forms are like digital paper forms, allowing users to input and submit data on websites. They are customizable and... This blog post assumes you are aware of PDF forms. If this is a new topic for you, check out our introductory blog post.... At IDR Solutions I spend a lot of time working on XFA for our Java PDF Library and PDF to HTML5 Converter and during... At IDR Solutions we spend alot of time working with XFA in our Java PDF Library. I have spent a lot of time working... This is one of our XFAarticles which investigates the important factors to be considered during the conversion from FormCalc script to Javascript (since none... 
