// https://www.youtube.com/watch?v=3FjYcMKZ3SU
function getFullscreenElement() {
    return document.fullscreenElement
        || document.webkitfullscreenElement
        || document.mozfullscreenElement
        || document.msfullscreenElement
}

$(document).ready(function () {
    $("#pdfViewer").kendoPDFViewer({
        pdfjsProcessing: {
            file: "https://demos.telerik.com/kendo-ui/content/web/pdfViewer/sample.pdf"
        },
        width: "100%",
        height: 1200,
        toolbar: {
            items: [
                {
                    type: "button",
                    togglable: true,
                    name: "myCustomTool",
                    icon: "fullscreen",
                    toggle: function (ev) {
                        var viewerElement = this.options.viewer.element[0];
                        if (getFullscreenElement()) {
                            document.exitFullscreen()
                        } else {
                            viewerElement.requestFullscreen();
                        }
                    }
                },
            ]
        }
    })
});