Thanks for taking interest in GroupDocs.Viewer API. Please note that GroupDocs.Viewer is a back-end, UI-less API which allows you to render the document as PDF document or in the form of HTML pages or images. When you render a document in HTML based rendering or image-based rendering, each page of the source document is converted into an HTML page or an image file. You will have to create your own front end application to view/display the HTML pages or images rendered by GroupDocs.Viewer.
You can implement this feature in your front-end application and restrict the user to copy the content when the rendered HTML page or the image is displayed (i-e in the browser).
This feature is also related to the front-end application where you can restrict the user to use print screen feature.
Currently, GroupDocs.Viewer does not support DZI file format. However, we shall check if there are any plans to provide its support in future.
Please mention the platform (.NET, Java or Cloud) for which you want to use the GroupDocs.Viewer API. It will help us to guide you more specifically.