Split a PDF in two

You can use pdftk, it's a handy tool for manipulating PDF documents.

sudo apt-get --yes install pdftk
pdftk foo-bar.pdf cat 1-12 output foo.pdf
pdftk foo-bar.pdf cat 13-end output bar.pdf

You can use this method to split a PDF in N ways, or to remove pages.

For example, to remove page 13:

pdftk in.pdf cat 1-12 14-end output out.pdf

Or use it to rotate pages and many other things, see man pdftk.

Installation is also possible by downloading a binary (Windows, OS X, Linux) or using Homebrew.

I know it is not exactly answer to your question, but trying to split pdf page by page got me here, so:

pdftk file.pdf burst output file-%d.pdf

And on Windows, you can easily install pdftk with chocolatey:

choco install pdftk

This can be done with cpdf:

cpdf in.pdf 1-12 -o out.pdf

cpdf in.pdf 13-end -o out.pdf

Or, to split into 12-page-sized chunks:

cpdf in.pdf -split -chunk 12 -o out%%%.pdf

Disclosure: I am the author of cpdf.

As my distribution doesn't package cpdf neither pdftk, I had to search for another solution and found the easiest one - in order to split PDFs, one can simply "print" page ranges from them, selecting PDF as an output (instead of a printer). This is for sure available in GNOME by default, but I am pretty sure that it is available in other DEs too.