PDF.JS - Detect when page has been rendered

Once PDF.JS has completed rendered each page, I want to then do a find/replace on the contents of that page.

I invoke PDF.JS by putting the following in a document in an iFrame:

<script>
fileId=0;
function getURLParameter(name) {
  return decodeURIComponent((new RegExp('[?|&]' + name + '=' + '([^&;]+?)(&|#|;|$)').exec(location.search)||[,""])[1].replace(/\+/g, '%20'))||null
}
var fileId = getURLParameter("fileId");
var DEFAULT_URL = '/viewer/fetchpdf.php?fileId='+fileId;
</script>

and then setting the URL from the parent frame:

url = '/_third_party/pdfjs/web/viewer.html?fileId='+$(this).attr('href');
$("#iframeViewPdf").attr('src', url);

I've noticed when using PDF.JS to render a PDF, it initialises each page with a loading placeholder:

<div id="pageContainer3" class="page" style="width: 991px; height: 1319px;">
    <div class="loadingIcon"></div>
</div>
<div id="pageContainer4...

It then renders the PDF as html, e.g.

<div id="pageContainer3" class="page" style="width: 991px; height: 1319px;">
    <div class="canvasWrapper" style="width: 991px; height: 1319px;">
        <canvas id="page46" width="991" height="1319" style="width: 991px; height: 1319px;">
        </canvas>
    </div>
    <div class="textLayer" style="width: 991px; height: 1319px;">
        ...
    </div>
</div>
<div id="pageContainer4...