/usr/lib/ruby/ is in ruby-pdf-reader 1.1.1-2.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/vendor_ruby/
/usr/lib/ruby/vendor_ruby/pdf/
/usr/lib/ruby/vendor_ruby/pdf/reader/
/usr/lib/ruby/vendor_ruby/pdf/reader/font.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/reference.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/object_hash.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/encodings/
/usr/lib/ruby/vendor_ruby/pdf/reader/encodings/pdf_doc.txt
/usr/lib/ruby/vendor_ruby/pdf/reader/encodings/mac_expert.txt
/usr/lib/ruby/vendor_ruby/pdf/reader/encodings/win_ansi.txt
/usr/lib/ruby/vendor_ruby/pdf/reader/encodings/mac_roman.txt
/usr/lib/ruby/vendor_ruby/pdf/reader/encodings/standard.txt
/usr/lib/ruby/vendor_ruby/pdf/reader/encodings/symbol.txt
/usr/lib/ruby/vendor_ruby/pdf/reader/encodings/zapf_dingbats.txt
/usr/lib/ruby/vendor_ruby/pdf/reader/abstract_strategy.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/object_cache.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/metadata_strategy.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/glyph_hash.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/glyphlist.txt
/usr/lib/ruby/vendor_ruby/pdf/reader/page_state.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/stream.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/xref.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/error.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/print_receiver.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/encoding.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/buffer.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/page.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/pages_strategy.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/text_receiver.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/page_text_receiver.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/object_stream.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/cmap.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/standard_security_handler.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/token.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/parser.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/lzw.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/resource_methods.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/form_xobject.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/filter.rb
/usr/lib/ruby/vendor_ruby/pdf/reader/register_receiver.rb
/usr/lib/ruby/vendor_ruby/pdf/hash.rb
/usr/lib/ruby/vendor_ruby/pdf/reader.rb
/usr/lib/ruby/vendor_ruby/pdf-reader.rb