How to merge 2 PDF files

On Lion (from memory, and I can't check anymore) this method:

• open PDF doc2 (with Preview),


• open PDF doc1 (with Preview),


• drag thumbnail from doc1 onto doc2,


• save as (⌘⌥⇧S) onto doc3

was an easy way to make:

doc3 = doc1 + doc2

or in Unix talk:

cat doc1 doc2 >doc3

Apparently (fixes appreciated) since Mountain Lion this simple receipe doesn't work anymore.

---

What is the easy way to achieve such a basic operation for PDF files:

• given 2 PDF documents doc1 and doc2,


• I want to get doc3 = doc1 + doc2,


• with as simple an application as Preview,


• within a few seconds of click, click, click….

I need this basic function for users running Mountain Lion, Mavericks, Yosemite.