You do not have to use top soil with Pennington Smart Seed Sun & Shade Mix Grass Seed, but you can. You just want a good smooth, somewhat firm seedbed when planting the Sun & Shade mix.
Pennington Smart Seed Sun & Shade Mix Grass Seed contains mainly fescues and a bluegrass, it should be a perennial grass that does not need to be reseeded every year.
The Pennington Smart Seed Sun & Shade Mix Grass Seed per the manufacturer has a blend of Fescue seed, 2 rebels and 1 birch, Kentucky Bluegrass, creeping and chewing.
If you are planning on overseeding with Pennington Smart Seed Sun & Shade Mix Grass Seed or any other seed, you can consider using a starter fertilizer to promote root growth and development. It is also recommended you do a soil test for more accuracy, but an example of a starter fertilizer is Ferti-Lome New Lawn Starter Fertilizer 9-13-7.