GTK3 documentation help files, known as the GTK+ 3 reference manual, can be installed on a Linux system providing a local copy of this reference. The advantage of installing the files locally on a system is that the documentation matches the version of the GTK+ 3 toolkit library that is installed on the system.
Installing GTK3 Documentation in Linux
To install the GTK+ 3 and GDK 3 reference manuals on a Debian Linux based computer such as Linux Mint or Ubuntu, enter the following in a terminal window.
sudo apt-get install libgtk-3-doc
On a Linux Mint system, the same package can be found and installed by searching for libgtk-3-doc in the Software Manager.
GTK+ 3 Reference Manual Location
After the reference manual package is installed, use a web browser, such as Firefox, to navigate to and open the manual at the following address.
GDK 3 Reference Manual
The GDK 3 manual can be found by using a web browser to navigate to:
On-line GTK3 Documentation
The newest GTK+ 3 and GDK 3 documentation can be found on-line, but may not correspond to the version number installed on a particular Linux system.
The following images show that the version number of the GTK+ 3 reference manual installed on a Linux system, which corresponds to the version number of the installed GTK+3 library is 3.10.8. On-line documentation at the same time is at version number 3.20.0.