Parts can have different shapes (if you want), but must have the same area.
You cannot use compasses, but you can use an unmarked straightedge if you want to make precise creases, or to avoid ripping the paper in an untidy fashion. You are not allowed to mark the straightedge, of course.
If the procedure were carried out with infinite precision, then it would indeed produce exact fifths.
Could you confirm or correct some guesses about exactly what problem is intended?
Folding is allowed.
The parts need to be of equal area but can have different shapes.
No other tools are allowed, not even “non-measuring” ones like an unmarked straightedge or a pair of compasses.
You want not an approximation but a procedure that, carried out with infinite precision, would produce exact fifths.
Folding is allowed, yes.
Parts can have different shapes (if you want), but must have the same area.
You cannot use compasses, but you can use an unmarked straightedge if you want to make precise creases, or to avoid ripping the paper in an untidy fashion. You are not allowed to mark the straightedge, of course.
If the procedure were carried out with infinite precision, then it would indeed produce exact fifths.