The -split operation splits a PDF file into a number of parts which
are written to file, their names being generated from a format. The
optional -chunk option allows the number of pages written to each
output file to be set.
If the output format does not provide enough numbers for the files generated,
the result is unspecified. The following format operators may be used:
%, %%, %%% etc.
Sequence number padded to the number of percent signs
