pdfrevert: 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/pdfrevert - from package: pdf-tools

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

On Debian possible default full paths are:

/usr/bin/pdfrevert - from package: libtext-pdf-perl

You may install the required package with command apt-get install {package}

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