unpaper: 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/unpaper - from package: unpaper

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

On Debian possible default full paths are:

/usr/bin/unpaper - from package: unpaper

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

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