"use strict";
var page = require('webpage').create(),
    system = require('system'),
    address, output, size;

if (system.args.length < 3 || system.args.length > 5) {
    console.log('Usage: rasterize.js URL filename [paperwidth*paperheight|paperformat] [zoom]');
    console.log('  paper (pdf output) examples: "5in*7.5in", "10cm*20cm", "A4", "Letter"');
    console.log('  image (png/jpg output) examples: "1920px" entire page, window width 1920px');
    console.log('                                   "800px*600px" window, clipped to 800x600');
    phantom.exit(1);
} else {
    address = system.args[1];
    output = system.args[2];
    page.viewportSize = { width: 600, height: 600 };
    if (system.args.length > 3 && system.args[2].substr(-4) === ".pdf") {
        size = system.args[3].split('*');
        page.paperSize = size.length === 2 ? { width: size[0], height: size[1], margin: '0px' }
                                           : { format: system.args[3], orientation: 'portrait', margin: '1cm' };
    } else if (system.args.length > 3 && system.args[3].substr(-2) === "px") {
        size = system.args[3].split('*');
        if (size.length === 2) {
            pageWidth = parseInt(size[0], 10);
            pageHeight = parseInt(size[1], 10);
            page.viewportSize = { width: pageWidth, height: pageHeight };
            page.clipRect = { top: 0, left: 0, width: pageWidth, height: pageHeight };
        } else {
            console.log("size:", system.args[3]);
            pageWidth = parseInt(system.args[3], 10);
            pageHeight = parseInt(pageWidth * 3/4, 10); // it's as good an assumption as any
            console.log ("pageHeight:",pageHeight);
            page.viewportSize = { width: pageWidth, height: pageHeight };
        }
    }
    // custom setup for changes_history page

    if (system.args.length > 4) {
        //page.zoomFactor = system.args[4];
        var cookie = system.args[3];
        var domain = system.args[4];
        if (!cookie || !domain) {
          console.log("Wrong session arguments");
        }
        else {
          phantom.addCookie({
            'name': '_trade_reporting_tool_session',
            'value': cookie,
            'domain': domain
          })
        }
    }

    page.viewportSize = {
      width: 1530,
      height: 2000
    };

    page.paperSize = {
      width: page.viewportSize.width,
      height: page.viewportSize.height,
      margin: '1.5cm'
    };

    page.open(address, function (status) {
        if (status !== 'success') {
            console.log('Unable to load the address!');
            phantom.exit(1);
        } else {
            window.setTimeout(function () {
                page.render(output);
                phantom.exit();
            }, 200);
        }
    });
}

"use strict";
var page = require('webpage').create(),
    system = require('system'),
    address, output, size;

function next_page(index, npages) {
  if (index == npages + 1) {
    console.log('Done!');
    phantom.exit();
  }
  var file = "/Users/leviathan/Desktop/Projects/trade_reporting_tool/changes_history_" + index + ".pdf";
  page.evaluate(function() {
    document.getElementById('next_page').click();
  });
  window.setTimeout(function() {
    page.render(file);
    next_page(index + 1, npages);
  }, 1000);
}

function handle_page(index, npages) {
  var file = "/Users/leviathan/Desktop/Projects/trade_reporting_tool/changes_history_" + index + ".pdf";
  page.open(address, function(status) {
    if (status !== 'success') {
      console.log('Unable to load the address!');
      phantom.exit(1);
    }
    else {
      window.setTimeout(function() {
        page.render(file);
        next_page(index + 1, npages);
      }, 1000);
    }
  });
}

address = system.args[1];
output = system.args[2];

var cookie = system.args[3];
var domain = system.args[4];
var npages = parseInt(system.args[5]);

if (!cookie || !domain) {
  console.log("Wrong session arguments.");
}
else {
  phantom.addCookie({
    'name': '_trade_reporting_tool_session',
    'value': cookie,
    'domain': domain
  });
}

page.viewportSize = {
  width: 1530,
  height: 2000
};

page.paperSize = {
  width: page.viewportSize.width,
  height: page.viewportSize.height,
  margin: '1.5cm'
};

handle_page(1, npages);

Update rasterize script to handle pagination