pure-pwconvert: 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/pure-pwconvert - from package: pure-ftpd

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

On Debian possible default full paths are:

/usr/bin/pure-pwconvert - from package: pure-ftpd-ldap
/usr/bin/pure-pwconvert - from package: pure-ftpd-mysql
/usr/bin/pure-pwconvert - from package: pure-ftpd-postgresql
/usr/bin/pure-pwconvert - from package: pure-ftpd

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

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