Few days back, an Ubuntu Xenial update has broken ImageMagisk ability to generate PDF and PostScript files. I realised it when my Nautilus PDF Generate script was not working anymore when dealing with conversion of multiple picture files to generate a single PDF document.
As image conversion was done using convert (from ImageMagick package), I checked convert behaviour when converting picture files to PDF. Here is the error message you get since last update :
convert: not authorized 'image.pdf' @ error/constitute.c/WriteImage/1028.
After some googling, I realised that ImageMagisk has recently gone thru some serious security flaws. These security flaws are quite serious for Web servers using ImageMagick for picture conversion. As an answer, some PDF generation restrictions have been implemented in Ubuntu repository for ImageMagick dfault policy.xml configuration file.
As ImageMagick PDF conversion feature is quite useful on an Ubuntu workstation, this article explains how to get back PDF generation functionality for convert utility. It also explains how to make it update proof in case of apt system updates.
It has been tested under Ubuntu Xenial 16.04 LTS and Ubuntu Bionic 18.04 LTS.
If you just want to recover PDF generation without all the explainations, you can jump to last section which provides a complete installation script.