I am searching the net how to remove ads from acrobat reader and I found nothing. After some investigation I found that reader checks the folloing registry value to decide whether to show ads or not:

[HKEY_CURRENT_USER\Software\Adobe\Acrobat Reader\6.0\AdsInReader]
"bShowAds"=dword:00000000 ; 0 - do not show, 1 - show, default - 1