pdnssec: 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/pdnssec - from package: pdns

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

On Debian possible default full paths are:

/usr/bin/pdnssec - from package: pdns-server

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

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