pdf2djvu: 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 Debian possible default full paths are:

/usr/bin/pdf2djvu - from package: pdf2djvu

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

Error in other languages:
pdf2djvu: bevel nie gevind nie
pdf2djvu: comandă negăsită
pdf2djvu: comando não encontrado
pdf2djvu: commande introuvable
pdf2djvu: command not found
pdf2djvu: käsku ei ole
pdf2djvu: không tìm thấy lệnh
pdf2djvu: komanda nerasta
pdf2djvu: Kommando nicht gefunden.
pdf2djvu: kommandot finns inte
pdf2djvu: komut yok
pdf2djvu: nie znaleziono polecenia
pdf2djvu: níor aimsíodh an t-ordú
pdf2djvu: no se encontró la orden
pdf2djvu: no s'ha trobat l'ordre
pdf2djvu: opdracht niet gevonden
pdf2djvu: parancs nem található
pdf2djvu: perintah tidak ditemukan
pdf2djvu: príkaz nenájdený
pdf2djvu: příkaz nenalezen
pdf2djvu: команда не найдена
pdf2djvu: командата не е открита
pdf2djvu: 命令找不到
pdf2djvu: コマンドが見つかりません