In order to suppress the Control+F key combination you need to handle the PreviewEditorKeyDown event as follows:
sender, Telerik.Windows.Documents.PreviewEditorKeyEventArgs e)
(Keyboard.Modifiers.HasFlag(ModifierKeys.Control) && e.Key == Key.F)
This will not disable the pop, but disable the key gesture associated with it. If you don't want this pop up to be usable by your clients remove the appropriate button in the RibbonView as well.
If you have any other questions get back to us.
the Telerik team
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