I'd say Pathfinder is way less heavy to run than D&D5e. The amount of pages is mostly due to two things:

1. Pathfinder ha a "rules over rulings" approach, so a lot of rules are codified and you don't need to know them: you just need to look them up when you find a situating you don't know how to resolve (the Archives of Nethys website is incredible for this).
2. Some things are spelled out multiple times rather than have a million "See page 524" references for a single paragraph rule.

The only things you need to run a successful Pathfinder game are:

1. Build the characters, following the order, with your players
2. Read the game mastering section
3. Trust that the game is balanced and the encounter builder does not disappoint

Finally, if you're still intimidated, just run an Adventure! The Beginner's Box is a great place to start easily even as a new GM, or if you're feeling you want a more ambitious campaign you can pick an Adventure Path (I recommend Age of Ashes).

You'll see that as soon as you just start paying everything fits quite seamlessly.

Just word of caution for players coming from 5e: the game expects teamwork and you using other actions than just attacking (Demoralize, in particular is an Action I recommend to new players). Just in general, it rewards you setting up the next player more than just going for them yourself.