pbmreduce: 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/pbmreduce - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pbmreduce - from package: netpbm

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

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