The easiest way to split, merge or edit pdf files in linux is to use pdftk.
sudo apt-get install pdftk
or
sudo aptitude install pdftk
or
sudo yum install pdftk
depending on what flavour of linux you have.
pdftk is quite powerful but, here are a few examples.
Split a multi-page pdf into separate files:
pdftk largepdfile.pdf burst
results in a number files like 0001.pdf, 0002.pdf, etc.
Merge files into one PDF file:
pdftk *.pdf cat output largepdfile.pdf
or
pdftk file1.pdf file2.pdf file3.pdf cat output largepdfile.pdf