No. For example a trapezium is not a square but it is a quadrilateral (a shape with 4 sides). But all squares are quadrilaterals.
It depends on what kind of shape it is. if it is a triangle, cut the shape in to two triangles, then find the square foot, if it is a quatrilateral, do the same thing.
The sum of all four angles is 360 degrees. Thus, you have insufficient information to know the individual angles; you can only know their sum, which is 360 minus the sum of the other two angles.
a polygon does not possess four sides and four angles, except for five and above. Therefore it is a quadilateral.