djvudigital: 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/djvudigital - from package: djvulibre

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

On Debian possible default full paths are:

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

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