Do you mean 'publisher' or 'producer'? I'll assume the latter.
A synopsis is a must, together with a running time, a cast-list, and an indication of how many cast members would be required to stage the production. If there are any unusual scenes that might pose a problem, these should also be mentioned.
It can also help is you can say why you're approaching a particular theatre company or producer. For example, if you've seen their work before and enjoyed it, it will do no harm to mention it.