trjconv: 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/trjconv - from package: gromacs

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

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