Quote - "PropViewer doesn't change the number of vertices and its position"

So sad, because that is what I want.

You have requested a tri to quad converter and this what PropViewer does, but this is not you want. You need something to do remeshing as decimation, simplification, gridification, etc and not conversion of tris to quads. If the final mesh has trinagles or quads is the less important thing. In most cases all the quads will be converted to triangles at rendering time.

Quote - It is better to work piece by piece instead of taking on the whole mesh at once.

This is correct. Any mesh processing method will fail if your mesh is not two-manifold. In your jacket there is a button that will complicate all, you must sepparate the button from the cloth. Sepparate as two groups or slit into two meshes and process each group/mesh alone.

Some remeshing methods also requires that the mesh cannot intersect itself.

 

Stupidity also evolves!