Thanks for your inquiry.
When you use the KeepSourceFormatting option and if a matching style already exists in the destination document, the source style is copied and given a unique name by appending a suffix number to it, for example “Normal_0” or “Heading 1_5”. On the other hand, you can use the UseDestinationStyles option. In this case, if a matching style already exists in the destination document, the style is not copied and the imported nodes are updated to reference the existing style.
Secondly, we have introduced RemoveUnusedResources method in Document class to remove any unused styles and lists from the document. Please see the following code:
Document doc = new Document();
I hope, this helps.