Lembro-me de procurar fazer a mesma coisa há alguns anos e eis que ainda tinha o link no arquivo profundo: http://forums.macrumors.com/showthread.php?t=1354754
Um membro do Fórum MacRumors chamado Oligarch reuniu várias ferramentas de PDF de linha de comando, que podem ser baixadas deste link: http://users.skynet.be/tools/
O comando pdfburst é o que você precisa:
NAME
pdfburst -- burst (split) PDF documents into single pages
SYNOPSIS
pdfburst file [path]
DESCRIPTION
The pdfburst utility bursts (splits) the PDF document file into single
pages which it writes to path, appended by an underscore character and
zero-padded page numbers.
If file is a single dash (-), the PDF document is read from the standard
input.
If path is omitted, the base name (last path component) of file is used
and the single page files are created in the current working directory.
If path ends with a slash (/), it designates a directory and the single
page files are named with just the page number.
Missing directories along path are created.