how do i make a pdf black and white in preview?
['Press Command-P to print your document.', 'Use the PDF menu and select “Open PDF in Preview”', 'Choose “Export…” from the File menu.', 'Ensure “PDF” is used as the output format.', 'Choose either “Gray Tone” (for grayscale) or “Black & White” from the Quartz Filter menu.', 'Save the document to your Desktop.']