I think there is major misunderstanding here.
The Primary-Interop-Assembly (PIA) is a bunch of .NET libraries for including reference to MS Office 2007+. It's for use of Office Automation as what you use for at the time of VB6. The primary advantage of using it instead of directly "Add reference" to the COM DLL is that, it's registered in the Global Assembly Cache (GAC) and it'll automatically load the correct version of Office for you (Many applications in MS Office allow side-by-side installation with earlier versions).
(1) Wrappers. This word appeared when I was trying to add a reference to Excel in a Visual Studio 2019 C# project (which should be easy). In the Reference Manager, Excel is mentioned in COM but not in NET assemblies (Community
edition). I found a dll file in my Windows 10 at C:\Windows\assembly\GAC_MISL... Microsoft.Office.Interop.Excel.dll. I Added that file and my C# project was satisfied. But when I mentioned this option in another forum, a person said
those dlls (I assume he referred to the GAC_MISL folder) are wrappers around the Office COM". From that I got the impression Office COM is older-style that need [help] wrappers to work with current .NET. So I'm curious if Microsoft
will update Office and Windows to .NET-assembly style dll.
(2) .dlla. Articles about .NET explain the new dll assemblies have metadata etc. that resolve problems with older-style dll. If they are that much different, I'm curious why they didn't assign a new extension.
Hi @George Seese ,
Hope the following reference is helpful for the first question.
Can I still use Microsoft.Office.Interop assemblies with office 2013?