Please see https://daq00.triumf.ca/DaqWiki/index.php/Ubuntu#Enable_elog_PDF_preview

see https://stackoverflow.com/questions/52998331/imagemagick-security-policy-pdf-blocking-conversion

xemacs -nw /etc/ImageMagick-6/policy.xml
remove this section at the end:
<!-- disable ghostscript format types -->
<policy domain="coder" rights="none" pattern="PS" />
<policy domain="coder" rights="none" pattern="PS2" />
<policy domain="coder" rights="none" pattern="PS3" />
<policy domain="coder" rights="none" pattern="EPS" />
<policy domain="coder" rights="none" pattern="PDF" />
<policy domain="coder" rights="none" pattern="XPS" />

K.O.