Zoom the current page by flZoom ( from 0.0 to 2.0, so to zoom to 120% use 1.2 ), zooming around point X,Y in the page (use 0,0 if you don't care)
public static void SetPageScaleFactor(HHTMLBrowser unBrowserHandle, float flZoom, int nPointX, int nPointY) { InteropHelp.TestIfAvailableClient(); NativeMethods.ISteamHTMLSurface_SetPageScaleFactor(unBrowserHandle, flZoom, nPointX, nPointY); }