I was troubleshooting an issue on a customer's workstation and found that, to my surprise, adodb.dll was nowhere to be found on the customer's workstation.
Typically, I see the file in C:\Program Files\Microsoft.NET\Primary Interop Assemblies folder.
Is this file distributed with the .NET framework or not?
Judging by MSDN, that file is written during a Visual Studio install.
Note Visual Studio.NET provides a Primary Interop Assembly (PIA) for ADO in the "Program Files\Microsoft.NET\Primary Interop Assemblies" directory in the file adodb.dll. If you have a copy of Visual Studio.NET installed, it is recommended that you use this file (adodb.dll) as opposed to importing your own using the Type Library Importer (tlbimp.exe).
I have this file on computers with VS installed, and don't have it on computers without VS installed. It looks like it should be pretty easy to generate your own with TlbImp.