page screenshot

No. Screenshots are exact shots of what you see on screen. There are some third-party programs that can do what you are asking, but Apple does not have an option for this as a screenshot. However, if the page is printable, then you can press Command-P to print the document, and then in the PDF menu choose the option to save the PDF to disk, or open it in Preview, or otherwise handle it, and this will represent the full contents of the page you are viewing (though formatted for the print page size, instead of the aspect ratio of your document on screen).