GIMP is one of many in the List of applications/Multimedia#Raster graphics editors.
Install the package.
Tip: The GIMP implements a plug-in system and the repositories (official, AUR) contain more plug-ins than listed in the package's optional depends.
GIMP PDF editing doesn't work
GIMP requires thelibrary for editing PDF files. Without this library GIMP will say that a PDF file is "unrecognized" when an attempt to open a PDF is made.