.NET core 3.0 and MS Office Interop

Question

I am trying to use the recently-released .NET core with MS Office using the interop assemblies

I've got a minimal project file

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp3.0</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.Office.Interop.Word">
      <Version>15.0.4797.1003</Version>
    </PackageReference>
  </ItemGroup>

</Project>

and this C# program

using System;
using Microsoft.Office.Interop.Word;
namespace ii
{
    class Program
    {
        static void Main(string[] args)
        {
            var app = new Application();
            Console.WriteLine(app.Version);
            app.Quit();
        }
    }
}

Unfortunately this fails with

Unhandled exception. System.IO.FileNotFoundException: Could not load file or assembly 'office, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c'. The system cannot find the file specified.
File name: 'office, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c'

When I added the package to the project I got this

warn : Package 'Microsoft.Office.Interop.Word 15.0.4797.1003' was restored using '.NETFramework,Version=v4.6.1, .NETFramework,Version=v4.6.2, .NETFramework,Version=v4.7, .NETFramework,Version=v4.7.1, .NETFramework,Version=v4.7.2, .NETFramework,Version=v4.8' instead of the project target framework '.NETCoreApp,Version=v3.0'. This package may not be fully compatible with your project.
info : Package 'Microsoft.Office.Interop.Word' is compatible with all the specified frameworks in project

implying 'compatible' but not 'fully compatible'

Is there a way to do this or must I use .NET Framework instead of Core?

I am using Windows 10, .NET core 3.0.100 and MS Office 365 (Word is version 16.0.11929.20298)

Possible duplicate of core 2.0 and office interop - where is the microsoft.office.core package? — GSerg
You get that warning every time you try to use a .NET Old assembly from .NET Core. It doesn't imply that the interop assemblies won't work. Have you tried using your application? — Panagiotis Kanavos
In any case, you don't need the interop assemblies to use COM. You can open Excel using late binding with dynamic excel = Activator.CreateInstance(Type.GetTypeFromProgID("Excel.Application", true)); and start using the Application object you get back - without type support. Interop assemblies make life a lot easier though by providing the CLSIDs and strongly-typed proxy object you'd otherwise have to create yourself. — Panagiotis Kanavos
I have tried using my application, and I get the FileNotFoundException mentioned above — Peter Hull
@PeterHull test silkfire's answer first though - that creates a COM reference with automatically generated proxy objects. They won't be as good as the interop assemblies (eg some parameters may be ints instead of enums) but they're definitely better than dynamic — Panagiotis Kanavos

silkfire silkfire · Accepted Answer · 2019-09-27T08:34:13

The solution to this is a bit quirky, but possible.

Create a new .NET Framework 4.X project. Add the relevant COM references to the project. Edit the .csproj of your .NET Core 3.0 project and add the generated references from the .NET Framework project to the <ItemGroup> tag.

It should look something similar to:

<ItemGroup>
    <COMReference Include="Microsoft.Office.Core">
      <Guid>{2DF8D04C-5BFA-101B-BDE5-00AA0044DE52}</Guid>
      <VersionMajor>2</VersionMajor>
      <VersionMinor>8</VersionMinor>
      <Lcid>0</Lcid>
      <WrapperTool>primary</WrapperTool>
      <Isolated>False</Isolated>
      <EmbedInteropTypes>True</EmbedInteropTypes>
    </COMReference>

... more references

</ItemGroup>

Do not use the NuGet packages, they are not compatible with .NET Core.

Update:

You can now add the COM references straight from the IDE (since Visual Studio 2019 v16.6):

.NET core 3.0 and MS Office Interop

5 Answers