hwp-thumbnailer: 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 Debian possible default full paths are:

/usr/bin/hwp-thumbnailer - from package: gnome-hwp-support

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