What is the easiest way to rearrange pages in a PDF document?

You can use PDF-Shuffler.

You can install it via terminal:

sudo apt-get install pdfshuffler

As shown in the image, you only have to import the PDF file you want to manipulate and drag & drop the pages in the desired order. It also lets you to rotate the pages in orthogonal angles.

You can save it in the same file or export it as a different PDF file.

You can install PDF-Shuffler using the following command:

sudo apt-get install pdfshuffler

The easiest way is to print the PDF to another PDF with a different page ordering. For example, if you want to reverse a 3 page PDF, you enter 3,2,1 under Pages.

Example