There is several ways how to add extensions into the IBM Notes client. But the best and simplest way that I have found is to do it this way.
Download the prefered Addon in my case I select the OpenNTF IBM XPages extension library, download the latest version to your computer. Unzip the file in your prefered location, Unzip the zipfile called updateSiteOpenNTF-designer.zip in a new folder.
In you Notes client create a new database in a folder on the server I call mine Client Updatessites and in the New database dialog select advanced templates and Eclipse Update site (9)
Give the database a name of that you like.
Open the database and click on Import Local update site find the site.xml in the client update site folder. (important it has to be the client update site) follow the steps when importing.
You might say, wait this is like installing this on the server, yes it is but we are adding client code in this case.
When you are done, go to the action menu and select show url:s a dialog appears.
Select the second option nrpc:// press the copy button besides this row.
Second step, importing the site into the client
On the right and side in you client there is a my Widget section
Click on the three lines at the right side
Now select Configure a widget from and then select Features and Plugins in a update site
paste the copied Url press load and press next selecting what you want to install , give the widget a good explaining name and finish.
you will also after a while get the approve install dialogs where you approve the installation.
After this your extension is ready to be used after a restart of the client. But the best thing is that you will get an icon in the “my Widget” section and if your right click that icon you can remove it. Send it to a collegue and an email or publish it to a widget catalog.
Easy simple administration of OpenNTF and other addons in the IBM Notes client & designer