mdconvert: 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/mdconvert - from package: isync

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

On Debian possible default full paths are:

/usr/bin/mdconvert - from package: isync

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

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