vipkhongtin markdown and bbcode formatting are supported in Flarum. If you copy some markdown or bbcode content, the formatting should stay similar to the source.
If you copy rich text from a webpage or World document and paste it into the composer, you'll get just the plain text. You could write an extension that converts rich text to markdown/bbcode. To my knowledge no such extension exists at this time.
If you need to do this operation a single time, I suppose there are some online tools to convert rich text from the clipboard to markdown which you could then copy to Flarum.
