How to Build a Bootstrap PDF Viewer with PDF.js

21 Jul 2020

author
Dustin Riley

In this article (a four-minute read), you’ll learn how to quickly build a PDF viewer with Bootstrap and PDF.js, a popular open-source PDF viewer.

Here’s what we’re going to build:

The source code for this project is available in our Git repo.

Prerequisites

Step 1 - Install http-server

We will be using http-server to run our website locally. To install http-server, run the following command from the Node.js command line:

npm install --global http-server

Step 2 - Create the Project Directory

Now we will create a simple project directory for our Bootstrap project. In your project folder create a folder structure that looks something like this:

pdfjs-bootstrap-project
├── public
│    ├── js
│    │   ├── index.js
│    ├── css
│    │   ├── index.css
│    ├── lib
│    │   ├── ...
│    ├── index.html
│    ├── form.html
│    ├── pdftron.html
│    └── ...
└── ...

All these files will be empty for now. We will populate them with content shortly.

Step 3 - Implementing PDF.js

We will now integrate the open-source PDF.js library into our project to render a PDF inside our app. We will start by downloading the latest stable release from GitHub and then extracting the contents into the public/lib folder.

We will also need a PDF file to view, which we will place in the web folder. You can use your own or download one from here.

The new file structure in our project folder will look like the following:

pdfjs-bootstrap-project
├── public
│    ├── js
│    │   ├── index.js
│    ├── css
│    │   ├── index.css
│    ├── lib
│    │   ├── ui
│    │   │   ├── ...
│    │   ├── core
│    │   │   ├── ...
│    │   └── webviewer.min.js
│    ├── index.html
│    ├── form.html
│    ├── pdftron.html
│    └── ...
└── ...

Step 4 - Create the Project

Next, we will make it so we can view the default viewer within our project. In the public/index.html add the following:

<!DOCTYPE html>
<html lang="en">

<head>
  <title>Bootstrap PDF.js Viewer</title>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/css/bootstrap.min.css">
  <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
  <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/js/bootstrap.min.js"></script>
</head>

<body>
  <ul class="nav nav-tabs">
    <li class="nav-item active">
      <a class="nav-link" href="/">About</a>
    </li>
    <li class="nav-item">
      <a class="nav-link" href="/form">Form</a>
    </li>
    <li class="nav-item">
      <a class="nav-link" href="/pdftron">PDFTron</a>
    </li>
    <li class="nav-item disabled">
      <a class="nav-link" href="#">Disabled</a>
    </li>
  </ul>
  <div class="row">
    <div style="height: 75vh" class="col-sm-6">
      <iframe height="100%" width=100% src='lib/web/viewer.html?file=pdf-js-express-default-doc-v2.pdf#zoom=40'></iframe>
    </div>
    <div class="col-sm-6">
      <div class="panel panel-info">
        <div class="panel-heading">
          <h3 class="panel-title">Bootstrap</h3>
        </div>
        <div class="panel-body">
          Bootstrap is a free and open-source CSS framework directed at responsive,
          mobile-first front-end web development. It contains CSS- and JavaScript-based design
          templates for typography, forms, buttons, navigation, and other interface components.
        </div>
      </div>
    </div>
  </div>
</body>

</html>

In the public/form.html add the following:

<!DOCTYPE html>
<html lang="en">

<head>
  <title>Bootstrap PDF.js Viewer</title>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/css/bootstrap.min.css">
  <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
  <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/js/bootstrap.min.js"></script>
</head>

<body>
  <ul class="nav nav-tabs">
    <li class="nav-item">
      <a class="nav-link" href="/">About</a>
    </li>
    <li class="nav-item active">
      <a class="nav-link" href="/form">Form</a>
    </li>
    <li class="nav-item">
      <a class="nav-link" href="/pdftron">PDFTron</a>
    </li>
    <li class="nav-item disabled">
      <a class="nav-link " href="#">Disabled</a>
    </li>
  </ul>
  <div class="row">
    <div style="height: 75vh" class="col-sm-6">
      <iframe height="100%" width=100% src='lib/web/viewer.html?file=form-demo.pdf#zoom=50'></iframe>
    </div>
    <div class="col-sm-6">
      <div class="panel panel-info">
        <div class="panel-heading">
          <h3 class="panel-title">Rendering a PDF with Bootstrap isn't difficult using open-source libraries.</h3>
        </div>
        <div class="panel-body">
          Building a PDF Viewer with Bootstrap is relatively straightforward,
          but once you want to start annotating, signing, or filling forms,
          you would have to implement these things yourself.
        </div>
      </div>
    </div>
  </div>
</body>

</html>

Also add in public/pdftron.html the following:

<!DOCTYPE html>
<html lang="en">

<head>
  <title>Bootstrap PDF.js Viewer</title>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/css/bootstrap.min.css">
  <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
  <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/js/bootstrap.min.js"></script>
</head>

<body>
  <ul class="nav nav-tabs">
    <li class="nav-item">
      <a class="nav-link" href="/">About</a>
    </li>
    <li class="nav-item">
      <a class="nav-link" href="/form">Form</a>
    </li>
    <li class="nav-item active">
      <a class="nav-link" href="/pdftron">PDFTron</a>
    </li>
    <li class="nav-item disabled">
      <a class="nav-link" href="#">Disabled</a>
    </li>
  </ul>
  <div class="row">
    <div style="height: 75vh" class="col-sm-6">
      <iframe height="100%" width=100% src='lib/web/viewer.html?file=demo.pdf#zoom=50'></iframe>
    </div>
    <div class="col-sm-6">
      <div class="panel panel-info">
        <div class="panel-heading">
          <h3 class="panel-title">PDFTron WebViewer.</h3>
        </div>
        <div class="panel-body">
          If you need high-fidelity rendering, increased reliability, and faster performance,
          you could consider PDFTron WebViewer.
          It’s a JavaScript PDF library that integrates
          with with many frameworks and offers hundreds of features, like redaction, editing,
          page manipulation, real-time document collaboration, digital signatures, and much more.
        </div>
      </div>
    </div>
  </div>
</body>

</html>

Make sure to change the PDF file names by adding custom PDFs to the lib/web folder and change all of the .html files by replacing the following with your PDF's file name:

 <iframe height="100%" width=100% src='lib/web/viewer.html?file=<YOUR-FILE.pdf>'></iframe>

We are importing Bootstrap from a content delivery network by adding the following in the <head> section:

  <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/css/bootstrap.min.css">
  <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
  <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/js/bootstrap.min.js"></script>

Bootstrap is a grid system that is based off of dividing the page into 12 columns so adding the class col-sm-6 means that the element will take up six of the 12 columns when the screen size is small (greater than 575px but less than 766px). It will continue to use 6 columns for screen sizes larger than this but when it is considered to be extra small (less than 576px) it will default to using all 12 columns. This is because we haven't specified any behaviour for extra small screen sizes. You can learn more about Bootstrap grid here.

Adding nav nav-tabs classes to a <ul> styles the tabs automatically to look like a header. To add items to the header just add the class nav-item to the child <li>. We can also display which page we are on by adding the class active to the <li> as well. Also adding the class disabled will make it look like the tab is inaccessible. You can read more about other Bootstrap tab styling here.

Similarly adding the panel panel-info classes creates the panel that is to the right of the PDF.js viewer. Adding the classes panel-heading and panel-title to the children of the panel element adds the heading and title respectively. You can also dictate the body by adding the panel-body class. If you want to learn more about Bootstrap panels you can read about that here.

Navigate to http://localhost:8080/ and you’ll see the default viewer and some navigation tabs which change the PDF being displayed:

Step 5 - Customizing the PDF.js Toolbar

As a final step, we will reorganize the toolbar by moving elements around, removing buttons, and changing the icons.

Let’s open public/lib/web/viewer.html and add the following to the <head> section:

<script src="customToolbar.js"></script>

Next, we’ll create customToolbar.js inside the public/lib/web folder and add the following code:

let sheet = (function() {
  let style = document.createElement("style");
  style.appendChild(document.createTextNode(""));
  document.head.appendChild(style);
  return style.sheet;
 })();
 function editToolBar(){
  //when the page is resized, the viewer hides and move some buttons around.
  //this function forcibly show all buttons so none of them disappear or re-appear on page resize
  removeGrowRules();

  /* Reorganizing the UI */
  // the 'addElemFromSecondaryToPrimary' function moves items from the secondary nav into the primary nav
  // there are 3 primary nav regions (toolbarViewerLeft, toolbarViewerMiddle, toolbarViewerRight)

  //adding elements to left part of toolbar
  addElemFromSecondaryToPrimary('pageRotateCcw', 'toolbarViewerLeft')
  addElemFromSecondaryToPrimary('pageRotateCw', 'toolbarViewerLeft')
  addElemFromSecondaryToPrimary('zoomIn', 'toolbarViewerLeft')
  addElemFromSecondaryToPrimary('zoomOut', 'toolbarViewerLeft')

  //adding elements to middle part of toolbar
  addElemFromSecondaryToPrimary('previous', 'toolbarViewerMiddle')
  addElemFromSecondaryToPrimary('pageNumber', 'toolbarViewerMiddle')
  addElemFromSecondaryToPrimary('numPages', 'toolbarViewerMiddle')
  addElemFromSecondaryToPrimary('next', 'toolbarViewerMiddle')

  //adding elements to right part of toolbar
  addElemFromSecondaryToPrimary('secondaryOpenFile', 'toolbarViewerRight')

  /* Changing icons */
  changeIcon('previous', 'icons/baseline-navigate_before-24px.svg')
  changeIcon('next', 'icons/baseline-navigate_next-24px.svg')
  changeIcon('pageRotateCcw', 'icons/baseline-rotate_left-24px.svg')
  changeIcon('pageRotateCw', 'icons/baseline-rotate_right-24px.svg')
  changeIcon('viewFind', 'icons/baseline-search-24px.svg');
  changeIcon('zoomOut', 'icons/baseline-zoom_out-24px.svg')
  changeIcon('zoomIn', 'icons/baseline-zoom_in-24px.svg')
  changeIcon('sidebarToggle', 'icons/baseline-toc-24px.svg')
  changeIcon('secondaryOpenFile', './icons/baseline-open_in_browser-24px.svg')

  /* Hiding elements */
  removeElement('secondaryToolbarToggle')
  removeElement('scaleSelectContainer')
  removeElement('presentationMode')
  removeElement('openFile')
  removeElement('print')
  removeElement('download')
  removeElement('viewBookmark')
 }
 function changeIcon(elemID, iconUrl){
  let element = document.getElementById(elemID);
  let classNames = element.className;
  classNames = elemID.includes('Toggle')? 'toolbarButton#'+elemID :
 classNames.split(' ').join('.');
  classNames = elemID.includes('view')? '#'+elemID+'.toolbarButton' : '.'+classNames
  classNames+= "::before";
  addCSSRule(sheet, classNames, `content: url(${iconUrl}) !important`, 0)
 }
 function addElemFromSecondaryToPrimary(elemID, parentID){
  let element = document.getElementById(elemID);
  let parent = document.getElementById(parentID);
  element.style.minWidth = "0px";
  element.innerHTML =''
  parent.append(element);
 }
 function removeElement(elemID){
  let element = document.getElementById(elemID);
  element.parentNode.removeChild(element);
 }
 function removeGrowRules(){
  addCSSRule(sheet, '.hiddenSmallView *', 'display:block !important');
  addCSSRule(sheet, '.hiddenMediumView', 'display:block !important');
  addCSSRule(sheet, '.hiddenLargeView', 'display:block !important');
  addCSSRule(sheet, '.visibleSmallView', 'display:block !important');
  addCSSRule(sheet, '.visibleMediumView', 'display:block !important');
  addCSSRule(sheet, '.visibleLargeView', 'display:block !important');
 }
 function addCSSRule(sheet, selector, rules, index) {
  if("insertRule" in sheet) {
  sheet.insertRule(selector + "{" + rules + "}", index);
  }
  else if("addRule" in sheet) {
  sheet.addRule(selector, rules, index);
  }
 }
 window.onload = editToolBar

The PDF.js primary toolbar is broken down into 3 regions:

Screenshot: PDF.js Viewer Primary Toolbar Regions

The secondary toolbar is accessed via the chevron icon in the right region:

Screenshot: PDF.js Viewer Secondary Toolbar

We can move elements from the secondary toolbar into the left, middle, or right regions of the primary toolbar with the addElemFromSecondaryToPrimary function in customToolbar.js. For example, uncommenting this line will move the counter-clockwise rotation tool to the left region of the primary toolbar:

  addElemFromSecondaryToPrimary('pageRotateCcw', 'toolbarViewerLeft')

If you wanted to move pageRotateCcw to the middle region instead, you’d replace toolbarViewerLeft with toolbarViewerMiddle, or toolbarViewerRight for the right region. To move a different tool, replace the pageRotateCcw ID with the element ID you want to move. (See below for a full list of element IDs.)

We can also hide elements like this:

  removeElement('print')
  removeElement('download')

To hide different elements, replace print or download with the element ID.

NOTE: Hiding the download and print buttons is not a bulletproof way to protect our PDF, because it’s still possible to look at the source code to find the file. It just makes it a bit harder.

We can also customize the icons for various tools by swapping out the SVG file, like this:

changeIcon('previous', 'icons/baseline-navigate_before-24px.svg')

In the above example, previous is the element ID, while icons/baseline-navigate_before-24px.svg is the path to the tool icon.

And that’s it!

Element ID Reference for PDF.js User Interface Customization

Here’s handy reference with the IDs of the various toolbar icons:

Toolbar Icon ID
PDF Viewer UI Icon: sidebarToggle sidebarToggle
PDF Viewer UI Icon: viewFind viewFind
PDF Viewer UI Icon: pageNumber pageNumber
PDF Viewer UI Icon: numPages numPages
PDF Viewer UI Icon: zoomOut zoomOut
PDF Viewer UI Icon: zoomIn zoomIn
PDF Viewer UI Icon: next page next
PDF Viewer UI Icon: previous page previous
PDF Viewer UI Icon: presentationMode presentationMode
PDF Viewer UI Icon: openFile openFile
PDF Viewer UI Icon: print print
PDF Viewer UI Icon: download download
PDF Viewer UI Icon: viewBookmark viewBookmark
PDF Viewer UI Icon: secondaryToolbarToggle secondaryToolbarToggle
PDF Viewer UI Icon: scaleSelectContainer scaleSelectContainer
PDF Viewer UI Icon: secondaryPresentationMode secondaryPresentationMode
PDF Viewer UI Icon: secondaryOpenFile secondaryOpenFile
PDF Viewer UI Icon: secondaryPrint secondaryPrint
PDF Viewer UI Icon: secondaryDownload secondaryDownload
PDF Viewer UI Icon: secondaryViewBookmark secondaryViewBookmark
PDF Viewer UI Icon: firstPage firstPage
PDF Viewer UI Icon: lastPage lastPage
PDF Viewer UI Icon: pageRotateCw pageRotateCw
PDF Viewer UI Icon: pageRotateCcw pageRotateCcw
PDF Viewer UI Icon: cursorSelectTool cursorSelectTool
PDF Viewer UI Icon: cursorHandTool cursorHandTool
PDF Viewer UI Icon: scrollVertical scrollVertical
PDF Viewer UI Icon: scrollHorizontal scrollHorizontal
PDF Viewer UI Icon: scrollWrapped scrollWrapped
PDF Viewer UI Icon: spreadNone spreadNone
PDF Viewer UI Icon: spreadOdd spreadOdd
PDF Viewer UI Icon: spreadEven spreadEven
PDF Viewer UI Icon: documentProperties documentProperties

Conclusion

As you can see, rendering a PDF with Bootstrap isn't difficult using open-source libraries.

Building a PDF Viewer with Bootstrap is relatively straightforward, but once you want to start annotating, signing, or filling forms, you would have to implement these things yourself. See our PDF.js Build vs Buy and Guide to Evaluating PDF.js to learn more.

That’s where PDF.js Express comes in. It’s a commercial PDF.js viewer that wraps a React-based UI around the open-source PDF.js rendering engine and offers out-of-the-box features like annotations, form filling and e-signatures. It’s fully compatible with many frameworks -- check out the demo, and let us know what you think!

If you need high-fidelity rendering, increased reliability, and faster performance, you could consider PDFTron WebViewer. It’s a JavaScript PDF library that integrates with many frameworks and offers hundreds of features, like redaction, editing, page manipulation, real-time document collaboration, digital signatures, and much more. Check out the WebViewer demo.

If you have any questions about implementing PDF.js Express in your project, please contact us and we will be happy to help!