When an element refers to a style name of a style that is not present in the document, trying to export it with RtfFormatProvider leads to KeyNotFoundException. A similar document could be produced when copying content from MS Word.

The same case is working properly with the other providers as well as in WordsProcessing (check the related 133762).

Workaround: Check all the styles used in the document and remove the NextStyleName or LinkedStyle values that point to non-existing in the document styles.

Available in LIB Version 2018.1.212.