There is no event that is fired when a new page is created. There is, however, a way to find out the current number of pages in the document and compare it to a predefined number.
In your handler of the DocumentContentChanged event of the RadRichTextBox, you can access the number of pages currently in the document and implement your desired behavior. This is an example:
sender, EventArgs e)
MAX_PAGES = 1;
(pages > MAX_PAGES)
As soon as you verify that the user has exceeded the limit, you can do whatever you like, e.g. undo the last action, show a warning, etc.
Hopefully that approach to the problem is suitable in your case.
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