qpdfview: 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/qpdfview - from package: qpdfview

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

On Debian possible default full paths are:

/usr/bin/qpdfview - from package: qpdfview

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

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