You cannot convert a single .ifo file to MP4, or any other video. However, you should be able to convert whole DVD media (.ifo, .vob etc.) to a single video format (like the MP4), with some dedicated DVD Ripper software specially designed for this job.
What it does is that it grabs and convert video data and saves them in one of the multimedia files, often compressed. This may lower the quality compared to the original.