Answer as of 2021 and version 11.
Adobe updates: Cannot be more convoluted
For years this software publisher with some poorly designed but intrusive products has acted with methods from the past. Modern competitors and open source software are especially welcome to make Adobe Reader a thing of the past, like Flash Player. That said for the moment Acrobat Reader is still to be dealt with as much as we can, us poor users. Be aware there are two options:
- Prevent updates the hard way.
- Prevent automatic updates and select another mode of update.
When disabling updates (first option), the "check for updates" entry in the application menu is also removed. While preventing automatic updates is legitimate, e,g. to close an open door for security concerns, preventing all updates forever is not a good idea anyway. It is used by large organizations which disable access to an update server and push new installers from their own infrastructure.
This is how Adobe sees the update process:

Configuration can done using a customization wizard which acts on the product installers directly, but it can also be done manually after the installation, by updating the keys in the registry.
Option 1: Customization wizard
The customization is intended to companies with volume licensing, and work prior to the installation, by configuring the installer. There are tons of pages in the help provided, but none directly related to update of Adobe Reader. So let's say goodbye to this first option.
Option 2: Manually disable any update (not recommended) bUpdater
.
Source.
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Adobe\Acrobat Reader\DC\FeatureLockdown\bUpdater
or
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Adobe\Acrobat Reader\11.0\FeatureLockdown\bUpdater
- Description by Adobe: Disables the Updater and removes associated user interface items.
- A DWord32. Set the value to 0 to disable the Updater.
Setting this key to 0 disable any update and remove any possibility to manually update using the menu. Note this setting is linked to the version of the reader, and will be ineffective after the next release, you'll need to change the key. Adobe's method.
Option 3: Select another mode of update than automatic: iCheck
and iCheckReader
Source.
iCheck
configures both Acrobat and Reader until 10.1. After 10.1,
use iCheckReader
for Reader.
HKLM\SOFTWARE\Wow6432Node\Adobe\Adobe ARM\1.0\ARM\iCheck
or
HKLM\SOFTWARE\Wow6432Node\Adobe\Adobe ARM\1.0\ARM\iCheckReader
Current version is 11 and iCheckReader
should be used for it. This key must be given a DWord value depending on the desired type of update, typically you may give a value of 4, corresponding to being informed of updates prior to deciding to download them:
0: Do not download or install updates automatically.
1: Do not download or install updates automatically.
2: Automatically download updates but let the user choose when to install them.
3: Automatically download and install updates.
4: (11.0 and later) Notify the user downloads are available but do not download them.