inpdfr package uses RGtk2 package for its GUI. Non-linux
users may need to download additional files such as the "gtk-file" icon, or
the "hicolor" theme, which can be found by downloading GTK+ from http://www.gtk.org/.
They are not needed for the GUI to work as intended, but you may get a "GTK-WARNING"
when using loadGUI(). Feel free to ignore this warning. The RGtk2 GUI is
not needed to access all funcionalities of inpdfr package. Some options
are only available through the command line interface.