When u save to the local, Revit will rename the 'original' to the same name with .001 in the name. Depending on your settings, you may find up to 5 of these. Example, ABC.RVT saves and then you will have ABC.001.RVT as well as the ABC.RVT. Then as subsequent saves are performed you could have ABC.001,RVT, ABC.002.RVT, ABC.003.RVT and so on. These 00x files are akin to the BAK.