file extension library at file-extension.com is very helpful in identifying the various extensions and understanding their uses. Also they have links to software that can improve the efficiency of our computer. The file extension vob is the format in which movies are stored in DVDs. In case you have a movie on a DVD then you can explore it and see that the movie is stored in the vob format. sis files can be found in mobile phones as they are found in the Symbian operating system. It is used as an extension for installer applications for the operating system.