SlackBuildsOrg/office/pdftk

If PDF is electronic paper, then pdftk is an electronic staple-remover, 
hole-punch, binder, secret-decoder-ring, and X-Ray-glasses. Pdftk is a 
command-line tool for doing everyday things with PDF documents.  Keep one 
in the top drawer of your desktop and use it to merge PDF documents, 
split PDF documents, apply watermarks, repair corrupt PDF, update PDF 
metadata, and more.  pdftk does not require Acrobat and is free software.

While not strictly required, you probably want to have the jdk package 
from extra installed (instead of L/jre) when building pdftk.