Hello. See, there is not much difference between the two. When the IIMs began, there was no provision for MBA, and hence they began giving padi degree. However, following the foreign trends, some new b-schools began with MBA degree, and it is wildly followed.
If you want to continue your studies in a foreign country, pgdm will play a spoilsport.
However, with the new IIM bill, IIMs will also award MBA degree, and the trend of pgdm degree might come to an end.

Hope this helps.

All the best