Since NAV 2015, it is possible to ship your solution as an extension. The benefit of using extensions compared to raw modifications using fob files is that the original objects delivered by Microsoft remain untouched. In theory, this should make it easier to upgrade as you don't have to merge your changes when Microsoft ships a new version of the core product.
Extensions are created using Windows PowerShell and have a list of restrictions and extra requirements.
We will create the WDTU application as an extension in Chapter 9, Successful Conclusions, and discuss the restrictions that come with this.
When programming for Dynamics 365 for Financials, extensions are the only way to deliver modifications for a Dynamics 365 system.