To combine two whole PDF records with each other, you should simply choose the PDF that you need to add to the ongoing PDF:

Open the first PDF you want to combine with Preview.

Step - 1

Click View and select Thumbnails to enable PDF thumbnails on the left.

Step - 2

Click the page you want to add your other PDF after on the left. To merge the entire PDF, just select every page.

Step - 3

Open the Edit menu at the top and click Insert > Page from File.

Step - 4

Choose the other PDF you want to merge with the current one.

Step - 5

Your PDFs should now be merged. Click on Export as PDF from the File menu to save your new merged PDF.

Step - 6