Pages from another document can be imported into the current PDF. 

  1. Drag & drop a PDF file onto your open document.
    or:
    1. With your destination PDF already open, choose Pages->Insert From Document... 
    2. Choose the PDF you wish to insert using the file selection dialog
  2. Select the pages to inset - All Pages or a range of pages.
    Insert Document options
  3. Choose the Placement - where the new pages should be placed in the current document
  4. To renumber the pages of your document, see Number pages