Creating a Form

The only way to add new pages to a PDF at runtime is with a Page Template. You'll find many posts on this topic. Here's a search link (not all posts are useful, you'll need to look thru them):

https://community.adobe.com/t5/forums/searchpage/tab/message?advanced=false&allow_punctuation=false&filter=location&location=forum-board:acrobat&q=Page%20Template

Page templates are created from the "Organize Pages" tool bar. 

If you created templates, you can spawn them by using  this as 'Mouse Up' action of radio button you wish to spawn template (just change template name to your actual template name):

var t1 = getTemplate("template name");
if (event.target.value != "Off"){
t1.spawn({nPage: numPages, bRename: false, bOverlay: false});}