imagemagick convert - split single multi-pdf to many pdfs

http://ardvaark.net/useful-pdf-imagemagick-recipes

Split single multi-pdf to many pdfs

$ convert -quality 100 -density 300x300 in.pdf multi%d.pdf

# combine, may increase in size by a lot
$ convert -density 150 pdf1.pdf pdf2.pdf out.pdf

or better
$ pdftk pdf1.pdf pdf2.pdf cat output temp.pdf