Run pdftk on Ubuntu 18.04 or later

The convenient pdf manipulation tool [cci]pdftk[/cci] is not available in Ubuntu 18.04 repositories because of some licensing incompatibilities. Using some docker magic and a small script we’ll use it as in previous Ubuntu releases, since it’s still available in 16.04 repositories. Here we will exploit the docker capabilities to run the [cci]pdftk[/cci] binaries in the…