> For the complete documentation index, see [llms.txt](https://docs.apryse.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.apryse.com/web/get-started/samples/showcase-demo-document-assembly.md).

# Document Assembly Showcase Demo Code Sample

Assemble PDF documents by dragging and dropping thumbnail pages between document viewers. This code relates to our showcase demo for documentation assembly.

{% hint style="info" %}
**Requirements**

*These packages are required to use these features in production. Trial keys have unlimited access to all features*

<a href="/web/get-started/readme.md" class="button primary">Web SDK</a><a href="https://apryse.com/capabilities#PageManipulation" class="button primary">Package: Page Manipulation</a><a href="https://showcase.apryse.com/document-assembly" class="button primary">Live demo</a>
{% endhint %}

Effortlessly assemble PDF documents by dragging and dropping thumbnail pages between document viewers. Perform manipulation securely in the memory of the browser without any server-side dependencies.

This demo allows you to:

* Upload your own PDF files
* Move thumbnail pages between viewers and merge them
* Edit the layout and content
* Download the merged PDF file

### **Implementation steps**

To add PDF assembly capability from two viewers:

Step 1: Choose your [preferred web stack for WebViewer](/web/get-started/readme.md) Step 2: Add the ES6 JavaScript sample code provided in this guide

Once you generate your license key, it will automatically be included in your sample code below.

{% @apryse-license-key/apryse-license-key platform="WEB\_VIEWER" variant="compact" %}

<pre class="language-js" data-line-numbers><code class="lang-js">// ES6 Compliant Syntax
// GitHub Copilot - Model: GPT-4o
// Date: July 14, 2025
// File: index.js

import WebViewer from '@pdftron/webviewer';

const licenseKey = '<code class="expression">visitor.claims.wvKey || "YOUR_WEBVIEWER_LICENSE_KEY"</code>'; // Demo requires a license key, get a demo license key from https://docs.apryse.com/core/guides/get-started/trial-key

// List of viewers with their configurations
// Each viewer can have its own document, alignment, size, instance, and merging features
let viewers = [
  {
    initialDoc: 'https://apryse.s3.us-west-1.amazonaws.com/public/files/samples/WebviewerDemoDoc.pdf',
    style: {
      alignment: 'Left',
      width: '49%',
      height: '100vh',
      margin: '0 auto',
    },
    instance: null,
    hasMerging: false, // The merging feature allows merging pages from one viewer to another
  },
  {
    initialDoc: 'https://pdftron.s3.amazonaws.com/downloads/pl/report.docx',
    style: {
      alignment: 'Right',
      width: '49%',
      height: '100vh',
      margin: '0 auto',
    },
    instance: null,
    hasMerging: true,
  },
];

// Customize the WebViewer UI
// Add custom buttons for merging (if merging feature is enabled) and downloading PDFs
function customizeUI(viewer) {
  const { UI } = viewer.instance;

  // Merge button
  let mergeButton = null;
  if (viewer.hasMerging) {
    mergeButton = new UI.Components.CustomButton({
      dataElement: 'mergeButton',
      className: 'custom-button-class',
      label: 'Merge Page',
      title: 'Merge the left WebViewer\'s first page, to be inserted prior to the right WebViewer\'s first page.',
      onClick: () => mergePage(), // Merge the pages
      style: {
        padding: '10px 20px',
        backgroundColor: 'white',
        color: 'blue',
        border: '1px solid blue',
      }
    });
  }

  // Download Pdf button
  let downloadButton = new UI.Components.CustomButton({
    dataElement: 'downloadPdfButton',
    className: 'custom-button-class',
    label: 'Download as PDF',
    onClick: () => downloadPdf(viewer.instance), // Download the PDF
    style: {
      padding: '10px 20px',
      backgroundColor: 'blue',
      color: 'white',
    }
  });

  let defaultHeader = UI.getModularHeader('default-top-header');

  // If the viewer has merging enabled, add the merge button and download button to the header
  // Otherwise, just add the download button
  if (viewer.hasMerging)
    defaultHeader.setItems([...defaultHeader.items, mergeButton, downloadButton]);
  else
    defaultHeader.setItems([...defaultHeader.items, downloadButton]);
};

// Merge the first page from the left viewer to be located at position #1 of the right viewer
// This function will be called when the merge button is clicked
// This function retrieves the source document, exports annotations, and inserts page(s) into the destination document
const mergePage = async () => {

  const srcDoc = await viewers[0].instance.Core.documentViewer.getDocument();
  const dstDoc = await viewers[1].instance.Core.documentViewer.getDocument();

  // get first page as a blob
  const xfdfString = await viewers[0].instance.Core.annotationManager.exportAnnotations();
  const data = await srcDoc.getFileData({
    xfdfString,
  });
  const arr = new Uint8Array(data);
  const blob = new Blob([arr], { type: 'application/pdf' });

  const docToInsert = await viewers[1].instance.Core.createDocument(blob, { extension: 'pdf', l: licenseKey });

  dstDoc.insertPages(docToInsert, [1], 1);
};

// Download the PDF
const downloadPdf = async (instance) => {

  // Get the filename from the document
  let filename = instance.Core.documentViewer.getDocument().getFilename();

  // Ensure it ends with .pdf. If not, replace it with .pdf extension
  if (!filename.endsWith('.pdf'))
    filename = filename.replace(/\.[^/.]+$/, '') + '.pdf';

  // Set the options for downloading the PDF
  const options = {
    filename: filename,
    flags: instance.Core.SaveOptions.LINEARIZED,
    downloadType: 'pdf'
  };

  instance.UI.downloadPdf(options);
};

// Create and initialize the WebViewer instances with their configurations,
// as many viewers are defined in the viewers list
function createWebViewer(viewer) {
  const element = document.createElement('div');
  element.id = `WebViewer${viewer.style.alignment}`;
  element.style.width = viewer.style.width;
  element.style.height = viewer.style.height;
  element.style.margin = viewer.style.margin;
  element.style.float = viewer.style.alignment;

  //find 'viewer' element in the body and append the viewer element to it
  const viewerElement = document.getElementById('viewer');
  if (!viewerElement) {
    console.error('Viewer element not found! Make sure the template execution area is ready.');
    return;
  }
  viewerElement.appendChild(element);

  WebViewer(
    {
      path: '/lib',
      initialDoc: viewer.initialDoc,
      loadAsPDF: true,
      enableFilePicker: true, // Enable file picker to open files. In WebViewer -> menu icon -> Open File
      licenseKey: licenseKey,
    },
    element
  ).then(instance => {

    // Enable merging pages feature from another WebViewer
    instance.UI.enableFeatures(instance.UI.Feature.MultipleViewerMerging);

    instance.Core.documentViewer.addEventListener('documentLoaded', () => {
      // Open the thumbnails panel
      instance.UI.openElements(['thumbnailsPanel']);

      // Select the first page in the thumbnails panel
      setTimeout(() => {
        instance.UI.ThumbnailsPanel.selectPages([1]);
      }, 500);

      console.log(`✅ ${element.id} loaded successfully.`);

      // Store the instance reference in the viewer object
      viewer.instance = instance;

      // customize WebViewer UI
      customizeUI(viewer);
    });
  }).catch((error) => {
    console.error(`❌ Failed to initialize ${element.id}:`, error);
  });
}

// Create the defined viewers in the viewers list
viewers.forEach(viewer => {
  createWebViewer(viewer);
});
</code></pre>

[View the full sample on GitHub](https://github.com/ApryseSDK/webviewer-samples/tree/main/showcase-demos-playground)


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