I have no idea why you are being so rude, but we’ll give it another shot.
Everything you’ve said in your clarification is fine. That is what Markdown is, and by extension that is what MultiMarkdown is. The latter has some extra features for book construction that Markdown does not address, as well as export formats that are useful to authors. Scrivener integrates these export methods into its compilation system. So you can use all of its organisational power on your project. The main difference is, of course, that when you are writing in the project you write using MultiMarkdown notation. Asterisks instead of bold and italics and so on. It will also convert footnotes and images to MMD syntax for you. After it has compiled your work into a single MMD text file, to a temporary location, it then runs the multimarkdown.exe utility to produce the output format you request in the compile settings. So you get your HTML file, an OpenOffice file, LaTeX and OPML. That’s what it does, so linking to the original Markdown definition and Fletcher Penney’s site is not a point of confusion. These systems do that, and Scrivener uses these systems in integration, so it does that as well (though not directly, it has the MultiMarkdown engine embedded in the installation so you don’t have to bother with installing it yourself).
But the whole system is predicated on the plain-text markup way of working. That means the stuff you import as well. Now we do have a planned feature for converting italics and bold to asterisks. This will be something you run on a document in the editor. But the import feature is for specifically importing MultiMarkdown text documents, not for importing rich text documents and converting them to MMD. It will take a plain-text MultiMarkdown document and convert it to Scrivener outline structure—it is thus very handy for round-tripping. You can compile a MultiMarkdown document, edit it elsewhere or have someone else edit it, then import it back in when this feature is enabled and get your original outline structure back. But it’s a plain-text importer (since it is importing plain-text files).
If you want to have your collaborator work with you using MMD, they need to use asterisks instead of their word processor formatting—or you need to convert it yourself. You might be able to find a tool or macro that can do this for you. I’ve never looked for one myself, but it strikes me as the sort of thing someone has probably done.
As for fixing the base formatting beyond italics and bold, we already have a feature for that which is useful to everyone, not just MMD users, because this problem with mismatching formats is of course quite common (and one of the things I dare say drives some people to MMD in the first place). The feature you want there is Documents/Convert/Formatting to Default Text Style
. This will retain inline formatting where sensible, like italics and bold, but fix up indents, font family & size, line-spacing and paragraph spacing. It’s a bulk tool, so you can run it on many selected documents at once.
So this was the source of my confusion. I took “marked up” literally in your statement on how the file was originally written, as in, it was already marked up with asterisks.