pbmtoppa: 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/pbmtoppa - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pbmtoppa - from package: netpbm

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

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