Project project = ...
OccWdBundle occurrence = ...

ActiveLibraryConnection activeLibrary = null;
IEnumerable<MaterialInfo> materials = null;
try
{
	activeLibrary = project.ActiveConnection;
	if (activeLibrary == null)
	{
		materials = MaterialInfo.GetPredefinedMaterials();
	}
	else
	{
		materials = activeLibrary.GetMaterials();
	}
}
catch (API.Exceptions.NoActiveLibraryException ex)
{
	materials = MaterialInfo.GetPredefinedMaterials();
}

MaterialInfo material = materials.FirstOrDefault(m => m.Name.Value == "My favourite material");
if (material == null)
{
	Console.WriteLine("Material not found.");
}
else
{
	occurrence.Material = material;
}