I've just install GIMP 2.8, and find there is choise to export image to PDF. But it doesn't work. I don't know why.
install Ghost Script.
Just Google it, and you will find it is a free program.
Gimp uses Ghost Script to open PDF and EPS image formats.
I thought that was auto integrated in 2.8?
"it doesn't work" is not an useful description of the problem. If we don't know what happens, then no one will be able to help.
Please check http://www.catb.org/~esr/faqs/smart-questions.html for useful hints about how to ask for help efficiently.