ftdiff: 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/ftdiff - from package: freetype-demos

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

On Debian possible default full paths are:

/usr/bin/ftdiff - from package: freetype2-demos

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

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