Canning pumpkin...option one
Cut the pumpkin in half and scoop out seeds. (keep for roasted seeds!) Then cut in to chunks, they don't have to be to small and put into a big pot. (see background)
I just kept going until my pot was full. Cover pumpkin with water and bring to a boil. Cook until fork tender. About as long as it take potatoes to cook.
Here's the time consuming part peel, scrape, or any other way take skin off pumpkin. Spoon pumpkin chunks out of water as you want to save the cooking water.
Put chunks of pumpkin into canning jars. After much research it is strongly suggested that for home canning of pumpkin you that you do not smash it. Pureed pumpkin is hard (nearly impossible) to get hot enough to safely can at home so according to all I read you should can it in chunks. It is easy to puree when you use it.
Now fill the jar with cooking liquid. Remember to leave an 1" head space. Put on lid and put in canner.
My canner has a line for where the water level should be which is only about a 3rd way up. Then turn on the heat to high and wait! When you see a steady stream of steam coming from the vent let vent for 10 mins. then put on the weight as seen above. :) Process (meaning cook) pints size jars for 55 mins and quarts for 90 mins. At 10 lbs pressure. For my canner that meant one ring. (check your manual)
Canning Pumpkin...option two
Option two is you can skip cooking the pumpkin first and peel the raw pumpkin pack in to jars and cover with boiling water and process the same. This cooks pumpkin in the canner while canning but I will warn you they both take the same amount of time as peeling or cutting the skin off raw pumpkin is not easy. As far as I can tell so far both yield pretty much the same result.