Select “Edit.” Tap on new” and then on flatten.” From the flatten” drop-down menu, choose either the method of flattening the PDF, the resulting PDF or both. Now tap on the add” or remove” buttons; then from the menu for this app, select the method that has been chosen for you. Flatten a PDF in Mac (OS X v10.11.2 and v10.10.5 Excluded) There is no way to flatten a PDF that has been modified by using any of these 3 methods. If you know of any other methods that can flatten a PDF in Preview, please let me know. This is useful information for people who like to use these methods to flatten PDF files in the hopes of getting better results. Please note that flattening a PDF file is not illegal, but should be treated with care and responsibility. The best flattening tool for Mac can get messed up when using these methods. This results in the flattening or saving process not working correctly. We all hate this! More Flat Pages To see the previous 7 pages of my book Flat Pages in PDF format, go here.