pdf2fax.gs: 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:

/var/spool/hylafax/bin/pdf2fax.gs - from package: hylafax+-client

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

On Debian possible default full paths are:

/var/spool/hylafax/bin/pdf2fax.gs - from package: hylafax-server

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

Error in other languages:
pdf2fax.gs: bevel nie gevind nie
pdf2fax.gs: comandă negăsită
pdf2fax.gs: comando não encontrado
pdf2fax.gs: commande introuvable
pdf2fax.gs: command not found
pdf2fax.gs: käsku ei ole
pdf2fax.gs: không tìm thấy lệnh
pdf2fax.gs: komanda nerasta
pdf2fax.gs: Kommando nicht gefunden.
pdf2fax.gs: kommandot finns inte
pdf2fax.gs: komut yok
pdf2fax.gs: nie znaleziono polecenia
pdf2fax.gs: níor aimsíodh an t-ordú
pdf2fax.gs: no se encontró la orden
pdf2fax.gs: no s'ha trobat l'ordre
pdf2fax.gs: opdracht niet gevonden
pdf2fax.gs: parancs nem található
pdf2fax.gs: perintah tidak ditemukan
pdf2fax.gs: príkaz nenájdený
pdf2fax.gs: příkaz nenalezen
pdf2fax.gs: команда не найдена
pdf2fax.gs: командата не е открита
pdf2fax.gs: 命令找不到
pdf2fax.gs: コマンドが見つかりません