How to texture a downloaded model made of stretched triangles? I'm a beginner in blender. Trying to texture a 3d furniture model which was downloaded from the manufacturer site. Geometry is made of stretched triangles. This causes problems of stretched texture which is visible on render.

I unwrapped the model with "smart uv project" but the geometry is still stretched
Is there any solution to texture it properly or I need to remodel it to make it quads?

What if I need to use dozens of real furniture models like this? 
Should I model everything from scratch in blender?

some pictures to explain:enter image description here
This is caused by N-gons and double vertices.

If you only need simple shading, go Object > Shade flat and disable Autosmooth.



You can also use Mesh > Clean up > Limited dissolve to merge flat faces.
Before any larger changes, the mesh should be properly repaired.