Frequently Asked Questions

Tim van der Meij edited this page Apr 25, 2016 · 81 revisions

Can I specify a different PDF in the default viewer?

You can modify the DEFAULT_URL variable in the web/viewer.js file or you can append the ?file= query string to the viewer URL, e.g. In the latter case, the PDF path/URL must be encoded using encodeURIComponent().

The viewer can be started without any PDF loaded by setting the DEFAULT_URL variable to empty string or via using ?file= parameter without any location specified. Use to load PDF later.

You can use raw binary data to open a PDF document: use Uint8Array instead of URL in call or the DEFAULT_URL variable value. If you have base64 encoded data, please decode it first -- not all browsers have atob or data URI scheme support. (The base64 conversion operation uses more memory, so we recommend to deliver raw PDF data as typed array in first place.)

Can I load a PDF from another server (cross domain request)?

Not by default, but it is possible. PDF.js runs with the same permissions as any other JavaScript code, which means it cannot do cross origin requests (see Same origin policy and an example). There are some possible ways to get around this such as using CORS (see also unsafe headers issue and Access-Control-Expose-Headers issue) or setting up a proxy on your server that will feed PDF.js the PDF file (example: Please notice that generic/demo viewer blocks this functionality if deployed not on domain to avoid content spoofing (see

What browsers are supported?

The goal is to support all HTML5 compliant browsers, but since feature support varies per browser/version our support for all PDF features varies as well. If you want to support more browsers than Firefox you'll need to include compatibility.js which has polyfills for missing features. Find the list of features needed for PDF.js to properly work and browser tests for those features at Required Browser Features. In general, the support is below:

Browser Supported Automated Testing Notes
Firefox Stable yes Windows and Linux
Chrome Stable yes Windows and Linux
Opera Stable yes none
Android limited none Android's Web Browser version 4.0 or below lacks a number of features or has defects, e.g. in typed arrays or HTTP range requests
Safari limited none Safari (desktop and mobile) lacks a number of features or has defects, e.g. in typed arrays or HTTP range requests
IE10+ limited none IE 10 or above may lack of features or may have defects.
IE9 limited none IE9 lacks a number of features and most notably typed arrays which causes subpar performance.
<=IE8 NO none IE8 and below are missing too many features to be supported.

What browsers have extensions (and where can I find install procedures)?

There are currently extensions for Chromium and Opera. The Chromium extension is maintained by a PDF.js contributor. To install the Chromium extension, please refer to the readme. The Opera extension can be found here.

The Firefox extension is not supported and marked as disabled for Firefox versions 35 and up. PDF.js is part of Firefox since version 19. The extension is mostly used by developers and for bringing a newer version of the PDF.js library to an older Firefox version. Users should uninstall the extension, revert the pdfjs.disabled configuration setting and set the Options -> Applications selection for PDF documents to the internal viewer to continue viewing PDFs with PDF.js in Firefox.

I know JavaScript and want to contribute to the project. How do I start?

First, you need to prepare your fork and setup the development environment. Don't forget to read the Contributing page. Second, make yourself familiar with the PDF format and PDF.js internals. Third, if you don't already have a certain issue you want to fix, choose one from the open issues labeled 5-good-beginner-bug. Last, submit a pull request for the review. During any part of the process we recommend to communicate with the PDF.js team on #pdfjs IRC channel at if you have questions or need to find a reviewer.

Is it possible to add annotations to a PDF?

PDF.js is mainly written for reading PDF files, not editing them. Because of that we don't yet support adding any kind of annotations. We do however support rendering a number of annotation types for viewing.

What are the PDF.js keyboard shortcuts?

(warning, the following list may be incomplete)


  • next page: n, j, right arrow key, click in presentation mode
  • previous page: p, k, left arrow key, Shift + click in presentation mode

The home, end, page up, page down and all arrow keys can be used to navigate the document.

Viewer controls

User interface buttons or ctrl + mouse wheel can be used to change the zooming level, but keyboard shortcuts are also available:

  • zoom in: ctrl + +, ctrl + =
  • zoom out: ctrl + -
  • restore normal zoom: ctrl + 0
  • rotate the document clockwise: r
  • rotate counterclockwise: shift + r
  • presentation mode: ctrl + alt + p (does not work in IE11)
  • toggle hand tool: h
  • move focus to the 'go to page' box: ctrl + alt + g

(replace ctrl with meta on some configurations)

Outline sidebar

  • After showing the sidebar, click on the "Show document outline" button (Show document outline) to show the document outline (if the PDF file has one).
  • Nested outline items can be expanded/collapsed by clicking on the triangles at the left of an item.
  • To expand/collapse all items under the selected item, press Shift while clicking on the triangle.
  • Double-click on the "Show document outline" button (Show document outline) to expand/collapse all outline items.

The PDF.js files are too big. Is it possible to obtain minified versions of the JS files?

You can build a minified version of PDF.js using the following command:

gulp minified

We use UglifyJS to minify the JS files. It is known that other minifiers might break PDF.js code if advanced options are used (see #710 or #2479). It's safe to use minifiers, such as Google Closure Compiler, in whitespace/comments removal mode.

Is there a pre-built version PDF.js available?

Yes. Please see page for details. Also the code for the website at is located in the "gh-pages" branch. You can clone it using git clone -b gh-pages pdfjs-gh-pages or download the archive.

There are also generic PDF.js library builds available at These builds can be installed via npm npm install pdfjs-dist or bower bower install pdfjs-dist.

PDF.js does not render my files correctly. Can I report an issue?

Yes. The issues are used to track both bugs filed by users and specific work items for developers. Try to file one issue per problem observed.

Please specify valid title (e.g. "Glyph spacing is incorrect" instead of "PDF.js does not work") and provide more details about the issue: link to the PDF, location in the PDF, screenshot, browser version, operating system, PDF.js version and JavaScript console warning/error messages. The issues that do not have enough details provided will be closed as invalid/incomplete.

I know that my PDFs are corrupted. Will PDF.js attempt to display it?

Yes. PDF.js will attempt to recover usable PDF data (pages, content or fonts) and display the document. Please report the issue (see above) and we will take a look.

I have a really great idea. Where is the best place to record it?

The best place is our mailing list. You can subscribe to it using or Google Groups. This way you will reach not only developers. As an alternative, you can join our weekly engineering meeting to discuss new ideas for the project.

The issue tracking system is designed to record a single technical problem. A bug report is something where a developer/contributor can work on. The GitHub issue tracker is not a good place for general, not well thought out or unworkable ideas. Most likely a discussion-type issue will not be addressed for a long time or closed as invalid.

I'm developing a custom solution based on PDF.js core library. Can you help me?

We are glad to hear that and will try to help you, but first check examples at and search existing issues. If this does not help, please prepare short well-documented example that demonstrate the problem and make it accessible online on your website, jsbin, etc. before opening a new issue or contacting us on the IRC channel -- keep in mind that just code snippets won't help us troubleshoot the problem. The issues that do not provide enough details will be closed as invalid/incomplete (see reporting issue above).

Please periodically check or subscribe to our mailing list to be informed about changes in the PDF.js architecture/design or security announcements.

What is a latest stable version of PDF.js?

PDF.js is a general-purpose library to parse and render PDFs. At the moment it's included in the number of projects such as Firefox, Firefox OS, Chromium Extension, etc. We are recording our changes to the library with Github pull requests. Also the log of the changes is available from the git log.

The version number consists of three digits: the major release number, minor release number and build number. Before version 1.2, the major and minor numbers were selected when some major milestone was reached. Currently, we are practicing semantic versioning, where a major version release means that we can introduce API-breaking changes and a minor version release indicates added functionality and backwards compatible changes. The build number is incremented by one each time a new commit is pushed to the master branch. As a sanity check, we accompany each version number with the SHA hash of the latest commit.

We are moving fast and trying to land as much good stuff as we can review and test. The generic viewer and development version of Firefox PDF Viewer extension always contain the latest PDF.js build and available for testing.

During cooldown period, about once or twice in 6 weeks, we push our library to the Firefox Nightly channel. We decided to tag/mark our master branch each time we do that, and at this point a beta release is created. To promote a latest beta to a stable release, we listen for feedback (via github, bugzilla, mailing list, or IRC) from the users and projects that use PDF.js library. If no critical issues (e.g. a build is unusable, majority of the documents cannot be rendered, etc.) appeared, we promote the build as stable. Otherwise we either discard the release by replacing it by new beta or redo the build with commits that will fix a critical issue.

What types of PDF files are slow in PDF.js? Can I optimize a PDF file to make PDF.js faster?

Typically, PDFs with a smaller file size will be rendered faster and it depends on how big a single page is. The amount of pages does not affect the performance. It's essential that you optimize your documents for the web. See Optimize a PDF from Adobe's website for more information. There are more improvement techniques that we can suggest:

  1. Avoid using high resolution images -- 150 dpi resolution for scanned images shall be enough for screens, especially for low powered devices;
  2. Try to use JPEG encoding for color images/photos in RGB colorspace when possible;
  3. Avoid using expensive compositions/effects such as transitions/masking -- flatten transparency;
  4. Avoid using PDF generators (or don't create content) that produce ineffective PDF output (e.g. LibreOffice creates a lots of tiny images for vector elements/pictures it does not understand);
  5. If there is such a setting, use web-optimized PDF output / linearization;
  6. Fix or don't produce corrupted PDFs that do not conform to the PDF32000 specification.