Merge small PDFS into one long document using Preview

All the ways to combine PDF files

Drag PDF contents

When the PDF contents is collapsed to show just the first page, click and drag it to another PDF window and drop it below the thumbnail that is there. All the pages are copied across.

Collapse the contents

Show the sidebar when viewing a PDF file and thumbnail images of the pages appear. Move the mouse over the title here and click the arrow that appears to collapse the contents.

Drag PDF files

Instead of opening all the PDF files, open the one that is to appear first. Collapse the contents in the sidebar, then drag PDFS from Finder and drop them under the PDF thumbnail in Preview.

Quick create PDF

A very quick way to merge PDF files into one is to select them all in the Finder window. Ctrl+click any of them and then select Quick Actions>create PDF. You can’t control the order though.