You can add captions to figures, equations, or other objects.

From the Office Open XML File Formats Specification: This element specifies the contents and positioning for captions which can be used to automatically label objects in a WordprocessingML document. A caption is a string that labels an object included in a WordprocessingML document, and typically consists of a string plus a field which numbers this item within a collection of similar objects.

Similar functionality can be achieved using the CustomCodeField:

RadFlowDocumentEditor editor = new RadFlowDocumentEditor(document);
using (Stream stream = File.OpenRead("Image1.jpg"))
{
	ImageInline image = editor.InsertImageInline(stream, "jpg");
	editor.InsertBookmark("Image", image, image);
}

editor.InsertBreak(BreakType.LineBreak);
editor.InsertText("Figure ");
editor.InsertField("SEQ Image", "Update Figure Number");