How to Use pdf.js

Try Google'ing pdf.js documentation

/* create the PDF document */

var doc = new pdf();
doc.text(20, 20, 'hello, I am PDF.');
doc.text(20, 30, 'i was created in the browser using javascript.');
doc.text(20, 40, 'i can also be created from node.js');

/* Optional - set properties on the document */
doc.setProperties({
  title: 'A sample document created by pdf.js',
  subject: 'PDFs are kinda cool, i guess',        
  author: 'Marak Squires',
  keywords: 'pdf.js, javascript, Marak, Marak Squires',
  creator: 'pdf.js'
});

doc.addPage();
doc.setFontSize(22);
doc.text(20, 20, 'This is a title');
doc.setFontSize(16); 
doc.text(20, 30, 'This is some normal sized text underneath.');

var fileName = "testFile"+new Date().getSeconds()+".pdf";
var pdfAsDataURI = doc.output('datauri', {"fileName":fileName});

NOTE: the "pdf.js" project mentioned here is https://github.com/Marak/pdf.js, and has been deprecated since this answer was posted. @Treffynnon's answer is about the still-active Mozilla project (https://github.com/mozilla/pdf.js) that most searchers will be looking for.

There is documentation available on their github readme. They cite the following example code:

/* -*- Mode: Java; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set shiftwidth=2 tabstop=2 autoindent cindent expandtab: */

//
// See README for overview
//

'use strict';

//
// Fetch the PDF document from the URL using promises
//
PDFJS.getDocument('helloworld.pdf').then(function(pdf) {
  // Using promise to fetch the page
  pdf.getPage(1).then(function(page) {
    var scale = 1.5;
    var viewport = page.getViewport(scale);

    //
    // Prepare canvas using PDF page dimensions
    //
    var canvas = document.getElementById('the-canvas');
    var context = canvas.getContext('2d');
    canvas.height = viewport.height;
    canvas.width = viewport.width;

    //
    // Render PDF page into canvas context
    //
    var renderContext = {
      canvasContext: context,
      viewport: viewport
    };
    page.render(renderContext);
  });
});