function merge() {
  var folder = DriveApp.getFolderById('<ID FOLDER>'); // folder with files pdf
  var files = folder.getFiles(); // get all files pdf
  
  var formData = {};
  var index = 0;
  while(files.hasNext()) {
    var file = files.next();
    formData['Files[' + index + ']'] = file.getBlob();
    index++;
  }
  
  var options = {
    'method' : 'post',
    'payload' : formData,
    'muteHttpExceptions': true
  };
 
  var response = UrlFetchApp.fetch('https://v2.convertapi.com/pdf/to/merge?Secret=<YOUR SECRET>', options);
  
  if(response.getResponseCode() == 200) {
    var contentText = JSON.parse(response.getContentText());
    var blob = Utilities.base64Decode(contentText.Files[0].FileData);
    folder.createFile(Utilities.newBlob(blob, 'application/pdf', 'merge.pdf'));
  }
}

var assingDestruction(){
const obj = { foo: 1, bar: 1 };
console.log({ ...obj, baz: 1 })
}

const obj = { a: 'a', b: 'b', c: 'c' };
Object.assign({ a: 1, b: null, c: void 0 }, obj); // { a: 'a', b: 'b', c: 'c' }
Object.assign({ a: 1, b: null }, obj, { c: void 0 }); // { a: 'a', b: 'b', c: undefined }
Object.assign({ a: 1 }, obj, { b: null, c: void 0 }); // { a: 'a', b: null, c: undefined }
Object.assign({}, obj, { a: 1, b: null, c: void 0 }); // { a: 1, b: null, c: undefined }

class MyClass {
  set val(v) {
    console.log('Setter called', v);
    return v;
  }
}
const obj = new MyClass();

Object.assign(obj, { val: 42 }); // Prints "Setter called 42"

Object.defineProperty(Object.prototype, 'myProp', {
  set: () => console.log('Setter called');
});

const obj = { myProp: 42 };

Object.assign({}, obj); // Prints "Setter called"

const newObj = { ..obj }; // Does **not** print "Setter called"

const obj = {};

Object.defineProperty(obj, 'myProp', {
  set: () => console.log('Setter called');
});
Object.assign(obj, { myProp: 42 }); // Prints "Setter called"

const Benchmark = require('benchmark');

const suite = new Benchmark.Suite;

const obj = { foo: 1, bar: 2 };

suite.
  add('Object spread', function() {
    ({ baz: 3, ...obj });
  }).
  add('Object.assign()', function() {
    Object.assign({ baz: 3 }, obj);
  }).
  on('cycle', function(event) {
    console.log(String(event.target));
  }).
  on('complete', function() {
    console.log('Fastest is ' + this.filter('fastest').map('name'));
  }).
  run({ 'async': true });

Object spread x 3,170,111 ops/sec +-1.50% (90 runs sampled)
Object.assign() x 3,290,165 ops/sec +-1.86% (88 runs sampled)
Fastest is Object.assign()

suite.
  add('Object spread', function() {
    ({ baz: 3, ...obj });
  }).
  add('Object.assign()', function() {
    Object.assign({}, obj, { baz: 3 });
  })

Object spread x 3,065,831 ops/sec +-2.12% (85 runs sampled)
Object.assign() x 2,461,926 ops/sec +-1.52% (88 runs sampled)
Fastest is Object spread