neotoppm: 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/neotoppm - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/neotoppm - from package: netpbm

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

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