Is there any way to take a piece of paper that is slightly crumpled/creased, and make it flat again?
I’m surprised they don’t have some sort of as-seen-on-TV type gadget to do this. Such as if you had something important (a newspaper clipping/picture/etc) that you wanted to preserve. It seems like trying to flatten it out only gets it so flat, the wrinkliness of it never seems to completely go away.
…you could try a cool iron, with no steam. Cover the paper with a cloth to be extra safe. As suggested in this thread regarding creased posters.
Well, just how badly crumpled is this paper? I think you should try it with an ordinary domestic iron - the gadget seldom used on the CelynClothes 
- at a low heat and see if that helps. I am sure it will, you know. I recall my brother, when young, doing the same thing to a scruffy school essay, and later did, myself, find that it worked.
UM…but you’ll remember the LOW HEAT bit?
Good luck.
Oddly enough, museums sometimes flatten crumpled documents by soaking in de-ionised water and laying them between two sheets of fine plastic gauze - I saw a TV programme where they used this method to restore a really valuable document (an original pencil sketch by LS Lowry, IIRC).
I’m not going to recommend it though - do it at your own risk.
It’s my understanding that folding and crumpling paper actually tears some of the fibers, so it’s not possible to completely remove the creases without drastic methods such as rewetting the paper and attempting to remat some of the fibers. This would seem to be a risky proposition, though…
Since paper was originally pulp that was dried and pressed this is might be the only method that will work. However, paper sometimes includes water soluble things, like some clay glazes, it isn’t quite the same piece of paper after it is soaked.
If this question is just curiosity, fine. If you actually have a valuable paper to restore, take it to an expert. Your librarian can probably find one for you.