/*

This InDesign script duplicates each page in place instead of appending the duplicates to the end of the document (e.g. 1-2-3 becomes 1-1-2-2-3-3)

*/

// Define variables
var file = app.activeDocument;
var pages = file.pages;
var numberOfPages = pages.length;

// Duplicate each page
for (var i = 0; i < numberOfPages; i++) {
  pages[i].duplicate();
}

// Intertwine pages
for (var j = 0; j < (numberOfPages - 1); j++) {
  var currentPage = (numberOfPages + j);
  var insertPoint = (j + j);

  pages[currentPage].move(LocationOptions.AFTER, pages[insertPoint]);
}