Embedded converter C - API needed

Hello everybody,
I am working on a kind of on the fly converter and I think that using LibreOffice may be the right choice, but I need your help to do so.

First of all, it is being developped as a C program, I got .doc, .docx, .odt etc. files in memory (not on the disk) and I need them to be converted into another format (let’s say I want all of them in .odt)

I would like to do so without having to write anything on the disk, nor running an instance of LibreOffice (or multiple).

Are there some kind of functions I could use from LibreOffice dynamic librairies that could do the requested job ? I could then import some of those functions to use them in my soft.

If not, what would be, in your opinion, the best way to convert large amount of file ? (I need something really fast, so avoiding writing to the disk would be great)

Thanks a lot,
Squall.