Ubuntu and Debian packages are compatible most times but not in all cases, i think this is the trouble you’re having you’re trying to use the Ubuntu’s .deb for Debian instead you should get the Debian specific file, (it works for both jessie and wheezy)
wget http://download.gna.org/wkhtmltopdf/0.12/0.12.1/wkhtmltox-0.12.1_linux-wheezy-amd64.deb sudo dpkg -i wkhtmltox-0.12.1_linux-wheezy-amd64.deb
Then in the /etc/init.d/openerp-server or /etc/init.d/odoo-server script(s), depending on your which one you have
add /usr/local/bin to the front of path environment variable for example,
PATH=/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin,
This tells odoo where to look for system binaries it requires or optionally you can copy the files to /usr/bin, if you don’t want to mess with those files
sudo cp /usr/local/bin/wkhtmlto* /usr/bin/
Src: http://stackoverflow.com/questions/38262173/how-to-correctly-install-wkhtmltopdf-on-debian-64-bit