https://code-industry.net/free-pdf-editor/

Create the following script in /usr/local/bin

/usr/local/bin/pdfupdate.sh

#!/bin/bash
if [ "$LOGNAME" != "root" ]
then
    echo "Master PDF Editor updater needs to be run as root!"
    exit
fi

#get latest pdf version number for qt 5.4.1 or later
url=$(curl -s "https://code-industry.net/free-pdf-editor/" \
    | grep "https://code-industry.net/public/master-pdf-editor-.*-qt5.x86_64.deb" | head -n 1 | cut -d '"' -f 2 | tail -n 1)
#get latest master pdf version on web
mpe_ver=$(echo "$url" | sed 's/.*\([0-9]\.[0-9]\.[0-9][0-9]\).*/\1/')

current_mpe_v=$(dpkg -s master-pdf-editor | grep -i version)
current_mpe_ver=$(echo "$current_mpe_v" | sed 's/.*\([0-9]\.[0-9]\.[0-9][0-9]\).*/\1/')

#convert version numbers to integers for comparison
mpemv=$(echo "$mpe_ver"         | sed 's/\.//g')
mpecv=$(echo "$current_mpe_ver" | sed 's/\.//g')
if [[ "$mpecv" == "" ]];
then
    mpecv=0
fi
#download and install only if web version greater than current version
#if main web version doesn't exist, then install new main version
if [[ "$mpecv" == 0 || "$mpemv" -gt "$mpecv" ]]
then
    echo "Current Master PDF Editor version $current_mpe_ver, upgrading to version $mpe_ver"
    cd /tmp/
    wget https://code-industry.net/public/master-pdf-editor-${mpe_ver}-qt5.x86_64.deb
    dpkg -i master-pdf-editor-${mpe_ver}-qt5.x86_64.deb
    rm master-pdf-editor-${mpe_ver}-qt5.x86_64.deb
else 
    echo "Current Version $current_mpe_ver, available version $mpe_ver"
    echo "No upgrade necessary"
fi

Make it executable

sudo chmod 755 /usr/local/bin/pdfupdate.sh

Create daily cron job:

/etc/cron.daily/pdfupdate

#!/bin/sh
echo `date` >> /var/log/pdfupdate.log
/usr/local/bin/pdfupdate.sh 2>&1 >> /var/log/pdfupdate.log 
echo >> /var/log/pdfupdate.log

Make executable:

sudo chmod 755 /etc/cron.daily/pdfupdate