It is possible to create a copy of the document by exporting and then importing
it with the XamlFormatProvider. It will create an identical copy of the document, however you should have in mind that all UIElements inside InlineUIContainer will be cloned and their settings might be different from the actual ones and event handlers might not work.
Another option for you may be to use Undo several times. This will be possible if you use the API of and commands of RadRichTextBox to modify the document only. Change made using the API of RadDocument are often not undo-able and document history would be cleared in these cases.
Let us know if you have more questions.
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