/usr/bin/pdf_callbacks
/usr/bin/pdf_list_callbacks
/usr/bin/pdf_object
/usr/bin/pdf_text
/usr/lib/ruby/gems/1.8/gems/pdf-reader-1.1.1/bin/pdf_callbacks
/usr/lib/ruby/gems/1.8/gems/pdf-reader-1.1.1/bin/pdf_list_callbacks
/usr/lib/ruby/gems/1.8/gems/pdf-reader-1.1.1/bin/pdf_object
/usr/lib/ruby/gems/1.8/gems/pdf-reader-1.1.1/bin/pdf_text
You may install this package on CentOS with
yum
install rubygem-pdf-reader