[abenedik]

I think that ply files define only the data for the mesh and not for the material.

If you want to preserve the material information, you will need to export to some other file format - for example fbx, obj or dea.

If this is not possible, then you will need to manually change the material of the loaded object - you can use the following code:
 

Code:

var imageBrush = new ImageBrush();
imageBrush.ImageSource = new BitmapImage(new Uri("fileName"));

// To read image from resource use the following (replace AssemblyName and FilePath)
//imageBrush.ImageSource = new BitmapImage(new Uri("pack://application:,,,/[AssemblyName];component/[FilePath]"));

var material = new DiffuseMaterial(imageBrush);

// Change material on the read readModel3D
Ab3d.Utilities.ModelUtils.ChangeMaterial(readModel3D, material, newBackMaterial: null);