changepdfstring: 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/changepdfstring - from package: libcam-pdf-perl

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

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