I agreed when it is taken as an adverb '的确' and '确实 is interchangable. ' Its english mening is indeed or really. However,确实 can be used as adjective as well. for eg: 确实的理由.

基本没有差别，但是的确的意思没有确实那么强，确实就是确定的真实，确实比较书面化，的确比较口语化。

usually they can change into each other , but anyhow the mood of "的确" only a little more intensity than "确实" ,for example:you are really stupid !and you are stupid definitely! hope you can get what's the difference.

I am a Chinese, tells you accurately, them has not distinguished

they have the same meaning