Win 10 Enterprise x64 on 4 machines, all configured similarly with fully-updated Acrobat DC. Office 2019 x64 installed but also LibreOffice 6.2 x32. Windows 10 updates delayed by 20 days; office updates turned off.
With in the past few days on 3 of the 4 machines the right-click option in the title disappeared. No amount of repairing of Acrobat made any difference to this and even a complete uninstall/reinstall made no difference. Searches identify this problem occurring but with no consistent reported solution.
I noticed that the problem only applied to office related file types, .doc, .docx, .rtf, etc. but not to others such as .odt or .txt where the right-click conversion option was retained.
On looking at the Computer\HKEY_CLASSES_ROOT\.doc in the registry and comparing a bad machine with the good one, I noticed that the Default subkey was blank on the bad machine but contained LibreOffice.Doc (my local preference) on the good machine. Simply setting the Default subkey to LibreOffice.Doc on the bad machines fixed the problem. For office users, I suspect setting it to the correct office file type name would also work. I repeated this for each of the defective file types with equal success (the name of the file type varies).
The reason why repairing Acrobat makes no difference is because the fault, in my case, had nothing to do with Acrobat. Something broke the office-associated subkeys in question. There had been a windows update about the same time but I cannot be certain it was causal.
I made a reg file to fix this (for LibreOffice users):-
"Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\.doc]
@="LibreOffice.Doc"
[HKEY_CLASSES_ROOT\.docx]
@="LibreOffice.Docx"
[HKEY_CLASSES_ROOT\.rtf]
@="LibreOffice.Rtf"
[HKEY_CLASSES_ROOT\.xls]
@="LibreOffice.Xls"
[HKEY_CLASSES_ROOT\.xlsx]
@="LibreOffice.Xlsx""
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