Unable to find Wkhtmltopdf on this system. The report will be shown in html. wkhtmltopdf.org
Here is the installation procedure...
wget https://github.com/wkhtmltopdf/wkhtmltopdf/releases/download/0.12.3/wkhtmltox-0.12.3_linux-generic-amd64.tar.xz
tar vxf wkhtmltox-0.12.3_linux-generic-amd64.tar.xz
cp wkhtmltox/bin/wk* /usr/local/bin/
Reference: https://learnopenerp.blogspot.com/2016/03/odoo-installation.html