Adobe has changed where you can choose to buy and not subscribe. Go to the following link and click on Buy next to Acrobat XI Pro: http://www.adobe.com/products/catalog/software._sl_id-contentfilter_sl_catalog_sl_software_sl_mostpopular.html. You will be able to change from Subscription to Full or Upgrade. Almir R V Santos.
If you think some malware is preventing the installation of Windows Defender definition updates, you may want to run a scan with Microsoft Safety Scanner or for more stubborn malware, using Windows Defender Offline. See how to update Windows 10 offline. These links are sure to interest you too:
Windows Defender is a part of your Windows 10 OS so you get it preinstalled in the system when you install the OS or buy the computer. It doesnât occupy extra space and cannot be removed from programs and features. You have no need to update Windows Defender separately as the update comes from this via Windows updates.