Hi David,

The wkhtmltopdf download packages for Ubuntu 18.04 or not by default working and enabled. You can resolve your issue with the following commands:

sudo wget https://builds.wkhtmltopdf.org/0.12.1.3/wkhtmltox_0.12.1.3-1~bionic_amd64.deb
sudo dpkg -i wkhtmltox_0.12.1.3-1~bionic_amd64.deb
sudo apt-get install -f
sudo ln -s /usr/local/bin/wkhtmltopdf /usr/bin
sudo ln -s /usr/local/bin/wkhtmltoimage /usr/bin

Afterwards restart your Odoo service and you should be able to print the PDF out fine..

P.S: Original answer was made at https://www.odoo.com/nl_NL/forum/help-1/question/ubuntu-18-04-lts-how-to-install-wkhtmltopdf-0-12-1-134198

Regards,
Yenthe