Convert RTF file to OPML

I have an RTF file created with Nisus Writer Pro that I would like to re-organize with OmniOutliner. I would like to be able to export or convert the H1, H2, H3, and H4 styles in the document to corresponding outlining levels. I want to then move sections around in the outline to plan a reorganization of the document. (I don’t want to then export anything back to RTF; this is just for a conceptual re-organization, and I’ll move everything in the original document.)

Is there any way I can do this, short of manually deleting all the rest of the content, or manually copying and pasting and the header styles? Thanks.

Been there.

Searching high and low came up empty. My issue was to copy outlines into scrivener. What I did find, before writing that 12000 line program (we had many other styles involved) was that pandoc had a lot of features, and that conversion via markdown or directly might be a possibility. Also, converting to indented text (csv or tab) has worked for moving into some mindmap software, but finding a way to move into opml directly is difficult. Finally, I find success for simple heading structured text by getting it into csv/tab and importing into OmniPlan (make sure that you get the correct line endings – I go via conversion to excel first) then from OmniPlan to OmniOutliner. Lot’s of tools needed to figure all this out, and I may not have seen every solution because I had way more complexity in the conversion effort.