Local $nPG = InputBox("Number", "Amount of pages?")
WinWaitActive("BOOK☆WALKER for Windows - Viewing screen")
Sleep(10000)
Local $i = 1
While $i <= $nPG
   WinActivate("BOOK☆WALKER for Windows - Viewing screen")
   Send("{PRINTSCREEN}")
   Sleep(1000)
   WinActivate("BOOK☆WALKER for Windows - Viewing screen")
   Send("{PGDN}")
   Sleep(1000)
   $i = $i + 1
WEnd