You could then use that image (you would probably want to clear the canvas to a white background color first otherwise you'll probably end up with a black background) when generating your PDF. But no native PDF export I'm afraid.
To clear the canvas to a white color you can either use the backgroundColor property if it's available or you can clear the canvas using an API function like this:
new RGraph.Rose({
id: 'cvs',
data: [1,2,3,4,5,6,7,8,9],
options: {
}
}).on('beforedraw', function (obj)
{
RGraph.clear(obj.canvas, 'white');
}).draw();