What is pdf2json-ruby?
It is a ruby installation wrapper for pdf2json. It comes bundled with 0.52 and installs as a gem. You can use Pdf2Json.bin_path to determine the path to the pdf2json executable.
This doesn't do any dependencies. You must have ghostscript, xpdf, etc installed ahead of time.
Why?
Because a pdf2json package wasn't available between OSX and various *nix OSes like Ubuntu.