mk4ht: 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/mk4ht - from package: tetex-tex4ht

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

On Debian possible default full paths are:

/usr/bin/mk4ht - from package: tex4ht

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

Error in other languages:
mk4ht: bevel nie gevind nie
mk4ht: comandă negăsită
mk4ht: comando não encontrado
mk4ht: commande introuvable
mk4ht: command not found
mk4ht: käsku ei ole
mk4ht: không tìm thấy lệnh
mk4ht: komanda nerasta
mk4ht: Kommando nicht gefunden.
mk4ht: kommandot finns inte
mk4ht: komut yok
mk4ht: nie znaleziono polecenia
mk4ht: níor aimsíodh an t-ordú
mk4ht: no se encontró la orden
mk4ht: no s'ha trobat l'ordre
mk4ht: opdracht niet gevonden
mk4ht: parancs nem található
mk4ht: perintah tidak ditemukan
mk4ht: príkaz nenájdený
mk4ht: příkaz nenalezen
mk4ht: команда не найдена
mk4ht: командата не е открита
mk4ht: 命令找不到
mk4ht: コマンドが見つかりません