htmldoc: 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/htmldoc - from package: htmldoc

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

On Debian possible default full paths are:

/usr/bin/htmldoc - from package: htmldoc

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

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