formal are like contracts or schedules aren;t they? ans informal all the covering letters and terms and conditions etc, Jenna would know but she's over in media !
... "formal" and "informal" are words which have no specific legal meaning, and are generally used to give (or take away) a suggestion of significance which, in reality, does not exist.
Yes...I just did a short Google search on 'formal documents', and it appeared to be a litereal minefield of opinions: cans of worms and spiders: et al.
Silverdaler, your question is to broad. If you require help, not always expert of course, you will have to give some indication of what type of documentation you are refering to. And as JJ said and dot alluded to, 'formal' and 'informal' are kind of meaningless.