Which of the following actions cannot be performed in Adobe Express?

The action of sending design files via snail mail cannot be performed in Adobe Express because the platform is primarily designed for digital content creation and sharing. It offers tools for designing graphics, videos, and other materials that can be easily shared online or downloaded for digital use. While you can export and save your designs as files suitable for printing, Adobe Express does not provide a direct feature for mailing these files physically.

In contrast, adding video clips, inserting images from stock libraries, and sharing projects with collaborators are all functionalities supported by Adobe Express. Users can enhance their projects with video content, access a library of stock images to include in their designs, and collaborate with others by sharing links to their projects or inviting them to edit directly within the platform. This focus on digital interactivity and collaboration makes physical mailing features outside the scope of what Adobe Express offers.