Currently RadRichTextBox supports only one section in its document. Even though you can declare and add numerous sections, they will be merged once the document is measured and arranged. That is why when you have several sections, the headers and footers declared for one of them are used in the whole document.
We will be introducing support for multiple sections in the near future (not in the upcoming Q2 release, but soon after that). Once multiple sections are supported, we would also implement the different headers and footers and the proper import and export.
All the best,
the Telerik team
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