How to Add a PDF Viewer & Editor to Salesforce as a Lightning Web Component

At PDFTron, we’ve worked with many clients who use Salesforce’s full-featured app framework to develop apps accessing the wealth of information stored in Salesforce databases. However, a number of these clients expressed frustration when trying to display and edit PDF documents within their web-based Salesforce solutions. Salesforce provides a few PDF offerings. But as we’ve written before: our clients found these problematic for a few different reasons.

So two years ago, we came up with an answer: a Salesforce-specific build of our pure JavaScript PDF viewing and editing SDK, WebViewer -- crafted to work around issues hosting libraries with Salesforce. This enabled users to open, view, edit and save PDF documents entirely within a Salesforce app. And now with the recent release of Salesforce Lightning Web Components supporting the latest versions of JavaScript, we were able to upgrade our Salesforce fix to support the latest version of WebViewer, ensuring even better rendering accuracy and access to the latest and greatest web features.

If you’re interested in plugging a professional PDF viewer into your Salesforce web experience -- read on! This article will show you how to add PDFTron WebViewer to Salesforce as a Salesforce Lightning Web Component.

linkGetting Started

To get started with WebViewer and Salesforce, you’ll first need to clone our sample Lightning Web Component project from Github. You can find the sample project here. You will also need to sign up for a free trial and then download WebViewer.

linkSetting up Salesforce DX

Next you’ll need to set up Salesforce DX for your organization through your Salesforce Dev Hub -- or by signing up for a Dev Hub trial. Follow the instructions in the Salesforce DX Setup Guide or in the App Development with Salesforce DX Trailhead module to get started. The steps include:

• Enable Dev Hub in your project
• Install the Salesforce DX CLI
• Install Visual Studio Code

linkOptimizing WebViewer Source Code for Salesforce

Now you need to optimize the original PDFTron WebViewer code for Salesforce. To accomplish this, extract the WebViewer.zip that you downloaded earlier into a folder and run this npm script:

$ npm run optimize

You will then encounter the following prompts, which you should answer y/n as indicated:

Optimize: Do you want us to backup your files before optimizing? [y/n]:  y
Optimize: Will you be using the new UI? [y/n]:  y
Optimize: Will you be converting all your documents to XOD? [y/n]: n
Optimize: Do you need client side office viewing support? [y/n]: y
Do you need the full PDF API? [y/n]:  n
Optimize: Do you need to deploy to salesforce? [y/n]:  y

After answering “y” to “Do you need to deploy to Salesforce?” the script will optimize and zip the source code you’ll need later.

Note that this optimization produces .zip files of no more than 5 mb in size -- small enough for safe upload to the Salesforce platform.

linkInstalling the Sample LWC App using Salesforce DX

Next you’ll need to clone our sample webviewer-salesforce project, configure it accordingly, and get it up and running. Follow these steps:

1. Clone the webviewer-salesforce from Github repo:

git clone git@github.com:PDFTron/webviewer-salesforce.git
cd webviewer-salesforce

2. Copy all the zip files generated after running the npm optimizing script from the output folder webviewer-salesforce into the force-app/main/default/staticresources folder of your newly cloned project.

Figure: The files you will need to copy from the “webviewer-salesforce” directory.

3. Add your license key in staticresources/myfiles/config.js. (Sign up for a free trial to get your license key).

4. If you haven’t done so, authenticate with your hub org and provide it with an alias (DevHub in the command below) from your terminal (macOS) or cmd (Windows).

sfdx force:auth:web:login --setdefaultdevhubusername --setalias DevHub

5. Enter your Dev Hub org credentials in the browser that opens. (You can close the browser after you log in successfully.)

6. Create a scratch org using the config/project-scratch-def.json file, set the username as your default, and assign it an alias.

sfdx force:org:create --setdefaultusername -f config/project-scratch-def.json --setalias my-scratch-org

7. Push the app to your scratch org:

sfdx force:source:push -f

8. Open the scratch org:

sfdx force:org:open

9. A browser will open where you should click the app launcher icon, and select PDFTron.

Here's the opened app:

linkImplementation Details for Developers

linkSetting Worker Paths in Config.js

Optimizing the original WebViewer source code for the Salesforce platform means that we will also have to set a few paths in config.js in order for WebViewer to function properly.

Open the config.js file in your myfiles folder and paste the following:

window.CoreControls.forceBackendType('ems');
window.CoreControls.setPDFWorkerPath('/resource');
window.CoreControls.setOfficeWorkerPath('/resource/office');
window.CoreControls.setPDFResourcePath('/resource/resource');
window.CoreControls.setPDFAsmPath('/resource/asm');

linkCommunicating with CoreControls from Lightning Web Component

On the Salesforce platform, Lightning Web Components have limited access to the WebViewer’s iframe due to LockerService requirements. However, with Lightning Components, you can still enable limited communication between components with the postMessage mechanism.

Here is implementation of the postMessage mechanism used in our sample project. You can use this approach to communicate with the iframe’s contentWindow.

Inside the config.js file, use the following:

window.addEventListener('message', receiveMessage, false);

function receiveMessage(event) {
  if (event.isTrusted && typeof event.data === 'object') {
    switch (event.data.type) {
      case 'OPEN_DOCUMENT':
        event.target.readerControl.loadDocument(event.data.file)
        break;
      default:
        break;
    }
  }
}

And in the Lightning Web Component, send messages with postMessage using the following:

import { LightningElement, track, wire } from 'lwc';
import myfilesUrl from '@salesforce/resourceUrl/myfiles';
import libUrl from '@salesforce/resourceUrl/lib';

export default class WebViewer extends LightningElement {
  
  handleFileSelected(file) {
    this.iframeWindow.postMessage({type: 'OPEN_DOCUMENT', file: file})
  }
  
  initUI() {
    const viewerElement = this.template.querySelector('div');
    const viewer = new PDFTron.WebViewer({
      path: libUrl,
      initialDoc: 'file.pdf',
      config: myfilesUrl + '/config.js',
    }, viewerElement);

    viewerElement.addEventListener('ready', () => {
      this.iframeWindow = viewerElement.querySelector('iframe').contentWindow
    });
  }
}

linkWrap up

That’s it! If you have any questions about implementing WebViewer in Salesforce, please feel free to get in touch and we will be happy to help!