How to calculate Joint CDF of joint PDF

I have 300 pairs of numerical data which depicts condition(roughness, energy) of 300 tumors.The information in the pair is independent of each other . I want to fit probability distribution on these pairs.Subsequently, I want to obtain the joint CDF.

Since the data is independent in each pair, I separated the energy values and roughness values from each other and fit distributions on each of them.The joint PDF is the product of the two fit distributions.Is there anyway i can obtain the joint CDF? I tried cdplot() but I am not sure if it the right answer.I also tried finding the individual cdf of each distribution and then took the product to find the joint CDF.The CDF reached up to 0.7 and not 1. Any help will be highly appreciated.

Thanks

[Jeff Miller]

What do you see when you make a scatterplot of the 300 (roughness, energy) pairs? The joint CDF will go up to 1 only if there is a point in the upper right corner of the scatterplot (i.e., a point with the maximum on both measures). The joint CDF is not required to go up to 1.