Add white background to appended page canvases

src/js/pdf.js

@@ -391,6 +391,10 @@ function addPage() {
     var prevPageCanvas = $("#page-canvas-container .page-canvas#pdf-canvas-page-" + (pageNumber - 1))[0];
     canvas.width = prevPageCanvas.getContext("2d").canvas.width;
     canvas.height = prevPageCanvas.getContext("2d").canvas.height;
+    var ctx = canvas.getContext('2d');
+    ctx.fillStyle = 'white';
+    ctx.fillRect(0, 0, canvas.width, canvas.height);
+
     $("#page-canvas-container").append(canvas);
 }