RadWordsProcessing currently doesn't provide such functionality, but I logged a Feature request in our public portal for it. Please, make sure to cast your vote for the implementation as well as subscribe to the task by clicking the Follow button so you can receive updates about status changes.
Fortunately, there is a way to implement splitting using the existing API and I made an example of how you can achieve the desired result. However, please keep in mind that this is only an example and you might need to modify it according to the specific case. We can accomplish the task using the DocumentElementImporter class to import document elements from one document to another. It also handles the style repository merging. You can read more in the Import Document Element help section.
I hope this helps.
Regards,
Martin
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