Unclear code licensing
While submitting #1, I noticed that the code licenses are also unclear. The COPYING file is the GNU GPL version 2, but a cursory inspection of source files reveals some Expat licensed files (e.g. https://gitlab.freedesktop.org/poppler/test/-/blob/master/buffer-diff.h), as well as a "main file" missing license information (https://gitlab.freedesktop.org/poppler/test/-/blob/master/test-poppler.c)