import win32gui
import win32con

global inum
inum = 1

def send_page_down(handle, param):
    global inum
    if win32gui.GetClassName(handle) == param and inum==14:
        win32gui.SendMessage(handle, win32con.WM_KEYDOWN, win32con.VK_NEXT, 0)
        win32gui.SendMessage(handle, win32con.WM_KEYUP, win32con.VK_NEXT, 0)
    inum+=1

window_id = win32gui.FindWindow(None, "Dport NOR SOF.pdf - Adobe Acrobat Pro DC")
win32gui.EnumChildWindows(window_id, send_page_down, 'AVL_AVView')