The wkhtmltopdf utility allows to convert web pages into PDF files. The utility does not come with a binary download for Slackware or for generic Linux distributions (this is explained on the download page). The download page lists some binary packages for specific Linux distributions such as Debian and CentOS.
However, the CentOS 6 package works very well on Slackware 14.1 after being converted to Slackware package format with the
rpm2tgz tool and after being installed.
Alternatively it can be installed from source by using the SlackBuild script. The compilation can take very long time.
There is also an alternative way to produce PDF files from web pages by using the PhantomJS screen capture functionality. The PhantomJS version 1.9 has static Linux builds. The 2.0 version has similar static build issues as wkhtmltopdf but the information in the issue comments gives hope that this will be resolved soon.