pdftk is missing from the official repository right now. That’s an issue for many people.
I needed PDFTK to be installed on Ubuntu (18.04) due to the need to manipulate PDFs. Unfortunately, because I used Laravel Forge, they only allow Ubuntu, and apparently PDFtk is not longer working with Ubuntu 18.04. There is a workaround! Follow the below to get it working.
There’s a workaround here: How can I install pdftk in Ubuntu 18.04 Bionic?
Quick and easy workaround
Try sudo snap install pdftk
Set up symlink so it works!
sudo ln -fs /snap/pdftk/current/usr/bin/pdftk /usr/bin/pdftk
The below seems not to work any more.
In SSH on your Ubuntu 18.04 server, do the below:
sudo dpkg -i pdftk_2.02-4build1_amd64.deb libgcj17_6.4.0-8ubuntu1_amd64.deb libgcj-common_6.4-3ubuntu1_all.deb
Then type ‘pdftk’, it should come up.
Hope that helps!