How can I combine two PDFs in Preview?
First, you can only merge pdf if they are not protected, if this is the okay :


Open both pdf
Enable the sidebar in each windows of Preview, then select "Thumbnails" view
Drag &amp; drop the cover (inside the sidebar) of one pdf into the sidebar of the other pdf.


With this method, you can completely merge two pdf or selectively drag &amp; drop the pages you want to merge to create a completely custom new pdf.

You can also extract pages from one pdf still using the same manipulation, but drag &amp; drop to the Desktop.