pnmtops: 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/pnmtops - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pnmtops - from package: netpbm

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

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