Convert and resize many PDFs to one PDF using a single command

1. Copy the PDFs you want some folder

2. Open Terminal in the folder or make a script and run the script in the folder.

.. the script

#! /bin/bash

convert -density 200 -trim *.pdf -quality 100 picture.jpg && mkdir PICTURES && find -iname “*.jpg” -exec mv {} PICTURES \; && convert -density 85 -trim PICTURES/*.jpg -quality 75 picture.pdf && rm -rf PICTURES

.. make script executable

+x convert.sh

Edit: If conversion does not work in Mint or an another Ubuntu-based distro, the reason is faulty /etc/ImageMagick-6/policy.xml file. In PClinuxOS has a workable file.