htmerge: 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/htmerge - from package: htdig

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

On Debian possible default full paths are:

/usr/bin/htmerge - from package: htdig

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

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