

You can rotate, delete and reorder pages from the thumbnail section, too. (If you have macOS Sierra or earlier, drag the thumbnails directly into a thumbnail in the other PDF.)

Check the permissions of a PDF by choosing Tools > Show Inspector, then click the lock icon). Some encrypted PDF documents can't be merged, according to Click Edit > Insert > Page from File (if the Page from File selection is dimmed so you can't click it, make sure that the file you have open is a PDF.Select the thumbnail for the page where you want to insert the other document.
