This part is the important part:
Once downloaded, extract the file. Opening the extracted directory, you will see a folder named
Packages.
Open that and you will findcnijfilter2_5.40-1_amd64.deb
You only need to double click the *.deb package - the installer will open a GUI popup window.
Gdebi is a .deb installation manager that I find to be a bit better than the Software Store at installation.
You can install it with
sudo apt install gdebi
Once done, you can set it as your preferred .deb package manager or you can just right click a .deb package and choose "Open with gdebi"
The Gdebi installer will open offering you choices to install or reinstall or remove - depending on if the package is already installed or not... And it will note any missing dependencies, if any.