libHaru is a free, cross platform, open source library for generating PDF files, and LuaHPDF is a module that lets you programmatically create PDF files via Lua using this library.
LuaHPDF was developed by Kurt Jung as an interface to the Haru PDF Library. I have built libHaru 126.96.36.199, with zlib 1.2.8 and libpng 1.6.2, and finally compiled the LuaHPDF 1.3.0 module.
A sample project features 16 different example routines, each showing different capabilities of the libHaru PDF library.
Documentation: libHaru Docs