extconv: 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/extconv - from package: texlive

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

On Debian possible default full paths are:

/usr/bin/extconv - from package: latex-cjk-chinese

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

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