pdfseparate: 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 Debian possible default full paths are:

/usr/bin/pdfseparate - from package: poppler-utils

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

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