What is a P F count, what are they for? Thank you.

P is how many letterboxes you’ve planted.
F is how many letterboxes you’ve found.
And if you come across X, that’s how many people you’ve exchanged signature stamps with.

Some people on AtlasQuest choose not to make their clues available to people who fall below a certain number of plants and/or finds.

P is plants and F is finds. these restrictions are used when a box is in an exposed area and sometimes state parks or other places that you maybe shouldn't be planting but cant resist due to a feature that grabs you.