txt2man: 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/txt2man - from package: txt2man

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

On Debian possible default full paths are:

/usr/bin/txt2man - from package: txt2man

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

Error in other languages:
txt2man: bevel nie gevind nie
txt2man: comandă negăsită
txt2man: comando não encontrado
txt2man: commande introuvable
txt2man: command not found
txt2man: käsku ei ole
txt2man: không tìm thấy lệnh
txt2man: komanda nerasta
txt2man: Kommando nicht gefunden.
txt2man: kommandot finns inte
txt2man: komut yok
txt2man: nie znaleziono polecenia
txt2man: níor aimsíodh an t-ordú
txt2man: no se encontró la orden
txt2man: no s'ha trobat l'ordre
txt2man: opdracht niet gevonden
txt2man: parancs nem található
txt2man: perintah tidak ditemukan
txt2man: príkaz nenájdený
txt2man: příkaz nenalezen
txt2man: команда не найдена
txt2man: командата не е открита
txt2man: 命令找不到
txt2man: コマンドが見つかりません