dngconverter: 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/dngconverter - from package: kipi-plugins

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

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