This straightforward solution (no need to install xvfb, neither compiling QT neither wkhtmltopdf) works like a charm on my Debian Jessie server :
cd mytmpfolder
wget https://github.com/wkhtmltopdf/wkhtmltopdf/releases/download/0.12.4/wkhtmltox-0.12.4_linux-generic-amd64.tar.xz
sudo tar xvf wkhtmltox-0.12.4_linux-generic-amd64.tar.xz
sudo mv wkhtmltox/bin/wkhtmlto* /usr/bin/
#create simple html test file
echo "<html><body>test</body></html>" >> test.html
#perform conversion
sudo wkhtmltopdf --disable-smart-shrinking --lowquality --enable-external-links --enable-internal-links test.html test.pdf