Combining pages from multiple PDFs is a matter of drag and drop between documents. If you have separate PDF files that contain pages you wish to use in another PDF, this technique is what you want.
Here’s how to create a new PDF from one or more existing PDFs:
Create a new, empty PDF document (see Make PDFs from Scratch).
Choose File > Open or File > Open Recent to open one or more existing PDF documents.
Show the thumbnail sidebar in all open document windows (described in Navigate with the Sidebar).
Drag one or more thumbnails from the sidebar of an open document to the sidebar of the blank document (Figure 5-5).
Figure 5-5. Add ...