How to Remove or Hide Sign In from Home, attached screenshot blue circle
Not possible in Adobe Acrobat DC.
Any Registry Key?
In Adobe Acrobat (paid for), you have to sign on to use it.
I'm guessing your question might actually about Acrobat Reader (free)?
Yes, it was for Adobe Acrobat Reader - Free Edition
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under "Computer\HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Policies\Adobe\Acrobat Reader\DC\FeatureLockDown\cServices", you have to create a new DWORD 32Bit with the value "bUpdater" and set theValue = "0"