RadRichTextBox and RadDocument do not use integer positions. This is so because the editor allows different types of rich content such as images and annotations, which cannot be counted easily. Some applications would require that they be counted as 1, others would expect them to be left out of the math, etc.
I suggest you look at the DocumentPositions article and the one about DocumentSelection which shows how DocumentPositions can be used.
The property CaretPosition of RadDocument is also an instance of DocumentPosition. You can manipulate it to move the caret at the places of the document where you would like to insert or delete text, as the methods of RadRichTextBox and RadDocumentEditor operate either on selection, or at the current position in the document.
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