Installing and referencing the Outlook PIA
You must have the Outlook Primary Interop Assembly (PIA) installed in the Global Assembly Cache (GAC) before you can incorporate information from the PIA in an Outlook managed add-in. By default, the PIA is installed automatically when you install Office on the development computer. However, if you need to install the PIA separately, see Configure a computer to develop Office solutions.
You must be an administrator on the development computer to install the Office PIAs.
After installation, if you are using Visual Studio to create the managed project, you can add a reference to the Microsoft Outlook 15.0 Object Library component. Subsequently, in the object browser, under the Microsoft.Office.Interop.Outlook namespace, you can see managed interfaces in the PIA that have names corresponding to objects in the Outlook object model.