Page turning function based on Windows API keyboard event

I would like to achieve Page Turning function for an opened PDF, based on Windows API keyboard event, however I've tried:

//Turn page up

HWND hWnd = ::FindWindow(NULL, _T("xxx.pdf - Adobe Acrobat Reader DC"));

HWND hWnd_c = ::FindWindowEx(hWnd,0,_T("AVL_AVView"),NULL);

int ret = ::PostMessage(hWnd_c, WM_KEYDOWN, VK_PRIOR, 0);

int ret2 = ::PostMessage(hWnd_c, WM_KEYUP, VK_PRIOR, 0);

However it didn't work, and I'd like to solve this issue.