pdf90: 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/pdf90 - from package: pdfjam

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

On Debian possible default full paths are:

/usr/bin/pdf90 - from package: texlive-extra-utils

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

Error in other languages:
pdf90: bevel nie gevind nie
pdf90: comandă negăsită
pdf90: comando não encontrado
pdf90: commande introuvable
pdf90: command not found
pdf90: käsku ei ole
pdf90: không tìm thấy lệnh
pdf90: komanda nerasta
pdf90: Kommando nicht gefunden.
pdf90: kommandot finns inte
pdf90: komut yok
pdf90: nie znaleziono polecenia
pdf90: níor aimsíodh an t-ordú
pdf90: no se encontró la orden
pdf90: no s'ha trobat l'ordre
pdf90: opdracht niet gevonden
pdf90: parancs nem található
pdf90: perintah tidak ditemukan
pdf90: príkaz nenájdený
pdf90: příkaz nenalezen
pdf90: команда не найдена
pdf90: командата не е открита
pdf90: 命令找不到
pdf90: コマンドが見つかりません