pgmtoppm: 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/pgmtoppm - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pgmtoppm - from package: netpbm

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

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