pjtoppm: 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/pjtoppm - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pjtoppm - from package: netpbm

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

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