Hi Stefan,
As you found out, RadPdfViewer already has a mode allowing to view a PDF one page at a time. On the other hand, the requirements you have seem somewhat specific to your application, so we are not planning on introducing another mode that will achieve this task. 
We believe that the implementation of the event logged in this item would allow you to prevent changing of the page and thus achieve the desired result. Alternatively, you can try creating a custom document presenter by following the steps outlined in this article: http://www.telerik.com/help/wpf/radpdfviewer-customization-and-extensibility-custom-document-presenter.html.