Cut and Fold Polyhedron! I have two convex polyhedra such that their sums of side areas are equal. It is true that I can cut one of them and flatten it on the plane, then fold the flattened polygon to reach the other polyhedron?
For special case in which these two polyhedra are cube and regular tetrahedron, The answer in Yes I think. But I think the answer is "No, not necessarily" in general case, and I think the problem is difficult!
 A: If this says what I think it says, the answer is "NO" for even the example cited, since you are prescribing the intrinsic metric on the polyhedron, and it is a celebrated theorem of A. D. Alexandrov (which is a slightly tweaked theorem of Cauchy) that the intrinsic metric determines the convex polyhedron uniquely. For more, see Alexandrov's "Convex Polyhedra"
A: The general answer is sometimes Yes, various unfold/refold pairs
of convex polyhedra exist, but not always,
depending on what is meant by "cut."
Here is an example that Erik Demaine, Marty Demaine, Anna Lubiw, and I worked out carefully:
The Latin-cross unfolding of the cube can refold
into precisely 23 distinct convex polyhedra,
as displayed below (all of the same surface area): 
the cube,
two doubly covered flat quadrilaterals,
seven tetrahedra,
three pentahedra, each with one or more quadrilateral faces,
four hexahedra,
and six octahedra:

 


 
Fig. 25.30, p.408 in Geometric Folding Algorithms: Linkages, Origami, Polyhedra, 2007.

Here is a "movie" of one of the refoldings to a tetrahedron:

 
 
 
 
 
 
 
 
 
 


But more generally, in the 2012 paper Refold Rigidity of Convex Polyhedra, we showed that every convex
polyhedron can be cut open and refolded to an incongruent convex polyhedron.

But if the cutting is restricted to follow edges of the convex polyhedron
("edge unfoldings"),
then there are "refold-rigid" polyhedra.
For example, each
of the 43,380 edge unfoldings of a dodecahedron may only fold back to
the dodecahedron.

Added.
I apologize for not initially understanding Morteza's precise question, which
asks whether or not, for any two given pair of convex polyhedra $P$ and $Q$
with the same surface area, is it always possible to cut
open $P$ and refold to $Q$. This remains an open question as far as I know.
It is a version of Open Problem 25.31 (Fold/Refold Dissections) in
Geometric Folding Algorithms. 
