Using Pumpkin in Beer Recipes                   

Reed  recommends the following:

Libby's® 100% Pure Pumpkin- all-natural & contains no preservatives (15oz. can) at a rate of approximately 3lbs per five gallon recipe ---ONLY in an all-grain recipe.

McCormick Pumpkin Pie Spice  ( Cinnamon, Ginger, Nutmeg, Allspice) 
or spices the brewer would rather use at a rate of 1 Tablespoon per five gallons at knockout (0 minutes)
& maybe once again at bottling.  Brewer's choice.

Dissolving the pumpkin in hot water to equally disperse in the mash.

If Using Fresh pumpkin - Bake for 20 to 30 minutes at 350º F. 
Your goal is to drive some moisture out.
By heating the pumpkin starch gelatinization will occur & starch can be converted to sugar in the mash.