pdfgrep: 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/pdfgrep - from package: pdfgrep

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

On Debian possible default full paths are:

/usr/bin/pdfgrep - from package: pdfgrep

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

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