At this point the Form Feed character is not supported in RadRichTextBox. We have this feature already logged in our backlog and you can vote and subscribe to the public item in Telerik's feedback portal
in order to track its progress.
In order to customize the presentation of the other symbols, you could implement a custom UI Layer. For more details on how to implement a custom layer you can refer to our SDK examples: Custom Layer and Custom Annotation
and Search and Highlight
Let me know if I can assist you with anything else.
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