I have already tested it. You can follow the steps below to add additional DLLs.

1.  Right-click the Packaging Project in Solution Explorer and select Add ➜ New Folde.

2. Right-click the new folder and select Add ➜ Existing Item.

3. Browse to DLLs that you need and add them to the project.

4. Once you install the application, the DLLs will be inside.