tcpdf_addfont: command not found

Have You tried accessing the binary with the full path?

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/tcpdf_addfont - from package: php-tcpdf

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