Changing font inside a rich text box paragraph without changing font of the whole paragraph

The problem may seem complicated, but I'll be the clearest possible. I need to be able to change the font everywhere in the text of a RichTextBox. For what I've seen so far, it is only possible to add content with a new font at the end of the paragraph. I would like to change the font a开发者_如何学JAVAt the cursor and start typing using the chosen font even if the cursor is in the middle of a word. All I could do is changing the font of the whole paragraph, taking the font of the surrounding characters or changing the font, but at the end of the paragaph. It is not a normal bahavior, and I go on thinking that doing that is ridiculously complicated...

Thanks for the help!

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just have a look at this post

How can I change the FontFamily in a WPF RichTextBox without modifying previous text