Our Web APP disables the intrinsic zoom function (e.g., by dragging with 2 fingers) to prevent text flowing outside the screen, which would require horizontal scrolling to read the whole line of text. Such design would be unacceptable to most users. The BSON Books Viewer provides its own method to enlarge text and images.
To magnify the text, simply change the font size from the setting.
Double clicks (or double taps) on an image will open the image in a new tab (or window) where you may use the intrinsic method to zoom in or out.