Google Chrome have the option \"Save as PDF\" when you enter the Print dialog or window.print(). The user need to choice this option in dialog to save the page as pdf.
Unfortunately there isn't any param you could pass to window.print(); and force it to print pdf unless there is a pdf driver plugin already present on the client's browser. There are plugins for firefox and IE (JS Print Setup and MeadCo Script respectively).
You may want to look at MrRio/jsPDF, a tool to generate pdf files at client-side JS.