The simplest method is resorting to a third party software. Many people like using programs like ImgBurn, PowerISO, CDBurnXP that do well in copying homemade and recorded DVDs. But as for those encrypted ones you bought, there may be nothing they can do. Different DVDs usually have different encryption techniques which make them hard to copy.
There is a good news. WonderFox DVD Ripper Pro - the most powerful DVD to ISO converter, is designed to copy even the most protected DVDs. You can copy DVDs and backup ISO image or digital files within only a few clicks. Over 300 formats and codecs are available as your choices to convert DVD files. But remember, before beginning to use, please make sure whether it is legal or not to copy DVD in your country.