pdf_object: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/pdf_object - from package: rubygem-pdf-reader
/usr/lib/ruby/gems/1.8/gems/pdf-reader-1.1.1/bin/pdf_object - from package: rubygem-pdf-reader

You may install the required package with command yum install {package}

Error in other languages:
pdf_object: bevel nie gevind nie
pdf_object: comandă negăsită
pdf_object: comando não encontrado
pdf_object: commande introuvable
pdf_object: command not found
pdf_object: käsku ei ole
pdf_object: không tìm thấy lệnh
pdf_object: komanda nerasta
pdf_object: Kommando nicht gefunden.
pdf_object: kommandot finns inte
pdf_object: komut yok
pdf_object: nie znaleziono polecenia
pdf_object: níor aimsíodh an t-ordú
pdf_object: no se encontró la orden
pdf_object: no s'ha trobat l'ordre
pdf_object: opdracht niet gevonden
pdf_object: parancs nem található
pdf_object: perintah tidak ditemukan
pdf_object: príkaz nenájdený
pdf_object: příkaz nenalezen
pdf_object: команда не найдена
pdf_object: командата не е открита
pdf_object: 命令找不到
pdf_object: コマンドが見つかりません