thumbpdf: 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/thumbpdf - from package: texlive-utils

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

On Debian possible default full paths are:

/usr/bin/thumbpdf - from package: texlive-latex-recommended

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

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