A heptagon is a plane figure and so has only one face.
Heptagonal is an adjective: the answer depends on the noun that it refers to. A heptagonal pyramid, a heptagonal dipyramid or a heptagonal prism or some other heptagonal shape?
Heptagonal is an adjective, not a noun! The answer will depend on whether you mean a heptagonal pyramid, a heptagonal bipyramid, a heptagonal prism or whatever.
A heptagon is a figure with 7 sides. Also, if by corner you mean edges, we can find that. There's the edges of the heptagonal base. So there's 7. Then we have the edges of where the lateral faces meet each other. There's another 7. You have 14 edges in a heptagonal pyramid. If, in fact, you meant "corners", then we add in the vertex (or apex) of the pyramid. Then you will have 15 "corners".
there is 13 edges in a heptagonal pyramid.
A heptagon is a 7-sided polygon, so a heptagonal prism is a 3D version of that (9 sides, 21 edges, 14 vertices).
A heptagonal prism has two 7-sided bases.