# Adding the external assembly .dll in UiPath Studio

> Make sure you test the project for errors before attempting to build it.

Make sure you test the project for errors before attempting to build it.

From the **Build** menu, select **Build Solution**. The `MathSquareOfSum.dll` library is now built and saved in the following location:

`%UserProfile%\source\repos\MathSquareOfSum\MathSquareOfSum\bin\Debug`

Once the library is built, the **Output** panel should display a message as depicted below:

![The Output panel for the MathSquareOfSum.dll.](https://dev-assets.cms.uipath.com/assets/images/sdk/sdk-the-output-panel-for-the-mathsquareofsum-dll-105408-50912f8d-967fe1b5.webp)

## Creating the NuGet package

1. Launch NuGet Package Explorer and click **Create a new package (Ctrl + N)**. A split-window is displayed which shows **Package metadata** and **Package contents**. We need to add all dependencies in the latter section.
2. Right-click inside the **Package contents** section. A context menu is displayed.
3. Select **Add lib folder**. Notice a new **lib** item is created in the **Package contents** section.
4. Right-click **lib** and select to **Add Existing File…**.
5. Load the external assembly (`.dll`) created above. In our case, the `MathSquareOfSum.dll` file is located in the `%UserProfile%\source\repos\MathSquareOfSum\MathSquareOfSum\bin\Debug` folder.
6. With the file selected, access the **Edit** menu and select **Edit Metadata**. The left panel is now fitted with editable metadata fields.
7. Fill in the fields as you see fit to better describe your custom activity.
8. Fill in the **Id** field. In our case, it can be **UiPath.MathSquare.Activities**, where the first value, **UiPath**, stands for the team which created the package. If no particular team was involved, the first value can be left blank.

   ![Providing values to properties of the MathSquareOfSum.dll](https://dev-assets.cms.uipath.com/assets/images/sdk/sdk-providing-values-to-properties-of-the-mathsquareofsum-dll-105404-5947b9e6-dd58c44c.webp)
9. Select the green check mark button in the top-left corner of the **Package metadata** section to save all changes.
10. From the **File** menu, select **Save As...**. An explorer window shows up, allowing you to choose the location of the new file.
11. Save the file in the folder where local packages are stored by UiPath (`C:\Program Files (x86)\UiPath\Studio\Packages` in versions prior to 2021.4 or `C:\Program Files\UiPath\Studio\Packages` starting with version 2021.4). The `UiPath.MathSquare.Activities.1.0.0.nupkg` file is now created in the `UiPath.MathSquare.Activities` folder inside the packages folder.

## Loading the NuGet package in Studio

1. Access the **Package Manager** from Studio.
2. Since we saved the NuGet package in the local packages folder, the activity should be available in the **Local** feed.
3. Search for the activity and click **Install** and then **Save**. The new activity is now installed and can be used in your automation projects.

   ![Your custom activity in UiPath Studio.](https://dev-assets.cms.uipath.com/assets/images/sdk/sdk-your-custom-activity-in-uipath-studio-105656-c0cef17e-33146222.webp)