As you know, GScan2PDF is an app for scanning pages and exporting them to PDFs. The user can export scans one by one, in separate PDF files, or export scans all together, in one PDF.
The latest version available is Gscan2PDF 1.7.3, which has been recently released, coming with a bunch of changes.
Up to date packages are available via some third party PPA, so installing the software on Ubuntu systems is easy. Add the PPA to your system, update the local repository index and install the gscan2pdf package:
$ sudo add-apt-repository ppa:jeffreyratcliffe/ppa
$ sudo apt-get update
$ sudo apt-get install gscan2pdf
Optional: To remove the gscan2pdf, do:
$ sudo apt-get remove gscan2pdf
The installation instructions should work on Ubuntu 16.04 Xenial Xerus, Ubuntu 14.04 Trusty Tahr, Linux Mint 18.x, Linux Mint 17.x, Elementary OS 0.3 Freya and other Ubuntu derivative systems.