I live in NW Pennsylvania and in the woods. I've tried everything to get grass to grow under the trees. I've put down peat moss and fertilizer and seed for shade but it won't take, I get just moss. Any suggestions?
Moss is due to lack of proper sunlight. You need to adjust your yard for that to fix the source of the issue.
Other than that, you should get the soil analyzed, it'll help you figure out what you need to amend in your soil to make it more fertile.
You may collect soil samples from various places around your yard and send it to your county's co-op extension (Penn State might have it). Once they analyze your soil, it'll give you measurement of your soil's pH level as well as Sulfur, Phosphorous, Calcium, Magnesium, Potassium, and etc. Once you know this, you can figure out what you need to add (e.g. lime, proper fertilizer(s), gypsum, and etc).
Best of luck
For the past twenty years I have lived under a grove of huge white oaks in North Carolina.
Its very shady.
The original builders of the home planted a very fine thin blade (almost hair like and now an heirloom) variety of red rye grass.
In places the yard is also moss covered. The oaks really do soak up the nutrients and water. I like way the the moss feels under my bare feet... the rye grass like to be kept cut short 2" vs the fescue stays tall 4"
This thread reminds me of the song by Rush "The Trees"
Have you tried raising the height of cut? Imagine you're a grass plant growing in shade. You need sunlight for photosynthesis, but there isn't much available due to the shade. On top of that, though, someone is coming along regularly and cutting off your precious photosynthesising leaves. Not a happy situation. Maybe rake off as much moss as possible then raise the height of cut to two inches and see how that goes.
You could try creeping red fescue. It does well in the shade.
Grass, any grass, does not like to grow in shady places, it really only does well in an open situation with plenty of sunlight, so I'm afraid whatever you do, short of cutting down or removing trees, grass is not an option in such a situation. Depending on how much light reaches the floor of the woods during the year, and whether the trees are deciduous or not, you might have some success with ground cover plants such as Pachysandra, but it does depend on the environment.