pbmtoptx: 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/pbmtoptx - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pbmtoptx - from package: netpbm

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

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