Duplicate PDF pages without blowing up the file size
You can duplicate pages in preview by opening up the sidebar to display thumbnails (View-&gt;Thumbnails), click on the page you want to duplicate, and then hold down Option and drag the thumbnail to the new location.  That will create a duplicate of the page and leave it at the new location.  When you do it this way, it does NOT duplicate the internal images and assets, but will reference them on the new page.  I just confirmed with a one-page PDF which had a 400k scanned image: I turned it into a 6-page document which was still around 400k.

If you instead add the page you wish to duplicate with Edit-&gt;Insert-&gt;Page From File... it loads all the assets again and does not reference the ones you'd already loaded, causing the file size to balloon.  It would certainly be nice if it could recognize that the assets are the same, but alas.