pdflatex: 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/pdflatex - from package: texlive-latex

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

On Debian possible default full paths are:

/usr/bin/pdflatex - from package: texlive-latex-base

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

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