Merging PDF pages using JavaScript

1WebViewer({
2  ... // other options
3  // when inserting pages from another document, the 'useDownloader' option should be false
4  url: '/url/to/first.pdf',
5  useDownloader: false,
6}, document.getElementById('viewer'))
7  .then(async instance => {
8    const { docViewer, CoreControls } = instance;
9    const doc = docViewer.getDocument();
10
11    const secondDoc = await CoreControls.createDocument('url/to/second.pdf');
12    const pagesToInsert = [4, 5, 6];
13    const pageIndexToInsert = doc.getPageCount() + 1;
14    // in this example doc.getPageCount() returns 3
15
16    doc.insertPages(secondDoc, pagesToInsert, pageIndexToInsert).then(() => {
17      doc.getPageCount(); // 6
18    });
19  });

1CoreControls.forceBackendType('ems');
2CoreControls.setPDFWorkerPath('/lib/core/pdf'); // path to web workers
3CoreControls.disableEmbeddedJavaScript(); // disabling pdf javascript
4
5// array of url of PDFs to merge
6const urls = [
7  'https://pdftron.s3.amazonaws.com/downloads/pl/demo-annotated.pdf',
8  'https://pdftron.s3.amazonaws.com/downloads/pl/Cheetahs.pdf',
9  'https://pdftron.s3.amazonaws.com/downloads/pl/magazine-short.pdf',
10];
11
12mergeDocuments(urls).then(mergedPdf => {
13  // merged pdf, here you can download it using mergedPdf.getFileData
14  
15});
16
17
18// recursive function with promise 
19function mergeDocuments(urlArray, nextCount = 1, doc = null) {
20  return new Promise(async function(resolve, reject) {
21    if (!doc) {
22      doc = await CoreControls.createDocument(urlArray[0]);
23    }
24    const newDoc = await CoreControls.createDocument(urlArray[nextCount]);
25    const newDocPageCount = newDoc.getPageCount();
26
27    // create an array containing 1…N
28    const pages = Array.from({ length: newDocPageCount }, (v, k) => k + 1);
29    const pageIndexToInsert = doc.getPageCount() + 1;
30    // in this example doc.getPageCount() returns 3
31
32    doc.insertPages(newDoc, pages, pageIndexToInsert)
33      .then(result => resolve({
34        next: urlArray.length - 1 > nextCount,
35        doc: doc,
36      })
37    );
38    // end Promise
39  }).then(res => {
40    return res.next ?
41      mergeDocuments(urlArray, nextCount + 1, res.doc) :
42      res.doc;
43  });
44}