zlib-flate: 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/zlib-flate - from package: qpdf

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

On Debian possible default full paths are:

/usr/bin/zlib-flate - from package: qpdf

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

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