How to load a file after build

Models, including their animations, are built into resource files when you build your stand-alone player. They are not actually loaded from separate files once the game is finally built.

To load files outside the normal Resources.Load pipeline post-build, you have to use AssetBundles. There is currently no other way to do so, short of writing your own content importer.

EDIT: Added more info on Asset bundles and how to load them.

AssetBundles are not created at runtime, they are created in the editor with an editor script. One would normally have to write this script oneself, but Unity made a sample editor script we can copy paste into our projects and use. It's available on this site, where you can also read in the docs about building AssetBundles:

http://docs.unity3d.com/Manual/BuildingAssetBundles.html

Copy paste that script into your project, then you can export your assets by rightclicking them and choosing Build AssetBundle From Selection. I only use the Track Dependencies version of it.

Afterwards, you now have an AssetBundle. This is a file that lives outside the normal Resources loading pipeline in Unity and can be loaded post build, which is what you require here. Loading them looks a little different from calling Resources.Load, but it's almost as simple. It can be done with few lines of code, I do it like this:

     AssetBundle assets = AssetBundle.CreateFromFile(Directory.GetCurrentDirectory() + "\\AssetBundles\\" + section.PartNumber + ".unity3d");
     assets.LoadAll();
     loadedObject = (GameObject)assets.mainAsset;

You have to supply your own path to AssetBundle.CreateFromFile, which is whereever you choose to store the .unity3d-file you originally exported using the editor script.

Hope that clears it up.