ImageMagick 6 uses policy.xml to set read/write permissions by file format. When read permissions are disabled for a format such as PDF, errors result like:

convert-im6.q16: not authorized

convert-im6.q16: DistributedPixelCache ‘127.0.0.1’

Fix

1. find policy.xml location at the top of

   convert -list policy

   for example on Linux it might be at /etc/ImageMagick-6/policy.xml

2. edit this policy.xml to have a line like:

   <policy domain="coder" rights="read" pattern="PDF" />