pdftools: command not found

Have You tried accessing the binary with the full path?

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/pdftools - from package: texlive-context

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