plt-help: 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 Debian possible default full paths are:

/usr/bin/plt-help - from package: racket

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

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