@ib130258 : make sure you decrypt the DVD as Toengel is telling. For sur this is important.

ISO files are more practical to move (to me), and put into a directory in the midle of mkv, avi, ...
ISO files are not converted, this is an image of you DVD. You can then burn them again and get an exact copy.
You can also attach jpg files to be used by XBMC for instance.
On Windows, VLC is also doing a good job.

To make iso, (again once decrypted if this is the case of your cource), you just need a burn software that lets you create ISO files instead of creating a real DVD. This is fast and easy and you archive original !