The 'mutool poster' command reads the input PDF file and for each page chops it up into x by y pieces. Each piece becomes its own page in the output PDF file. This makes it possible for each page to be printed upscaled and can then be merged into a large poster.

mutool poster [options] input output

The command line options are:

-x decimation factor
Pieces to horizontally divide each page into.
-y decimation factor
Pieces to vertically divide each page into.
Input PDF file name.
The output pdf file name.