Recently we installed Odoo 9 Community Edition on a fresh Ubuntu server.  When attempting to print a sales order, which creates a pdf version, it was creating a 0kb empty file. After attempting to update to various newer versions of wkhtmltopdf, we were able to resolve the issue. We ended up using whtmltopdf 0.12.2 version which resolved the issue for us.

Download the correct wkhtmltopdf 0.12.3 package your Ubuntu install (32 vs 64 bit) from http://download.gna.org/wkhtmltopdf/0.12/0.12.2/ . We use 64 bit version.

wget http://download.gna.org/wkhtmltopdf/0.12/0.12.2/wkhtmltox-0.12.2_linux-wheezy-amd64.deb

Install the package:

dpkg -i wkhtmltox-0.12.2_linux-wheezy-amd64.deb

Install dependencies:

apt-get -f install

Create symlinks in /usr/bin folder:

ln -s /usr/bin/local/wkhtmltopdf /usr/bin/wkhtmltopdf
ln -s /usr/bin/local/wkhtmltoimage /usr/bin/wkhtmltoimage