To use RadRichTextBox as a rich content viewer you have to disable the user from editing its content. This is done via the IsReadOnly property. You just have to set it to true.
[XAML] Example 1: Disable editing
<telerik:RadRichTextBox x:Name="radRichTextBox" IsReadOnly="True" />
In addition to the ReadOnly property, there are several other properties that can be used to control the response of RadRichTextBox towards the user actions against it:
IsEnabled - setting this property to False will disable the entire control. The user won't be able to enter any input in it and to scroll the contents.
IsSelectionEnabled - setting this property to False will disable the user to perform any selection inside the RadRichTextBox control.
IsFocusable - setting this property to False will exclude the RadRichTextBox control from the tab navigation.