Combine part of a PDF with another PDF in preview in mac

Combine part of a PDF with another PDF
Open the PDFs that you want to combine in Preview.
In each document, choose View > Thumbnails to show page thumbnails in the sidebar.
Press and hold the Command key ⌘, select the page thumbnails that you want to add to the other document, then release the key.
Drag the selected thumbnails into the sidebar of the other PDF, then release where you want them to appear.