I just discovered that pasdoc has a GUI. However, I didn't find a target to build it in the main Makefile. I think that is a pitty.
The commands to build pasdoc_gui were hidden in a "make dist-prepare" target :)
I just separated them into simple "make build-gui" target, mentioned also by "make help". Note that building the GUI requires Lazarus LCL, it calls lazbuild to build package+project.