Combine PDFs in Preview on Mac
Combine all or part of two or more PDFs into a single PDF.
WARNING: Changes you make to a Preview document are saved automatically. If you want to keep the original PDFs (in addition to the new combined one), choose File > Duplicate to create a copy of each PDF before combining them.
In the Preview app
on your Mac, open the PDFs you want to combine.In each open PDF, choose View > Thumbnails to display the page thumbnails in the sidebar.
Drag the thumbnails you want to add (Command-click to select nonadjacent pages) to the thumbnail sidebar in the other PDF.
You can add pages to the end of the document or between pages in a document. Drag thumbnails to reorder them.
Tip: To add an entire PDF to the beginning or end of another PDF, drag the PDF icon in the Finder to the sidebar of an open document.