djvuextract: 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/djvuextract - from package: djvulibre

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

On Debian possible default full paths are:

/usr/bin/djvuextract - from package: djvulibre-bin

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

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