Are there online some free adventures that I can download as .pdf? (Not piratery, just free adventures.) I'm a new GM and I'd like to read some professional adventures to see how they work. I need a short urban-style adventure, level 1. Any Ideas?
You have two main places that will have something like what you're looking for.
On the Paizo store, there is an adventure finder, go into e.g. 1st level adventures and sort by "Price, low to high." You'll basically see the two free RPG day adventures and the three PFS starter adventures. Real professional adventures don't come free.
On RPGNow, you can search for free Pathfinder adventures. You'll get more, though for some alternate definition of "professional" - not to knock these various authors, but it's not the same as Paizo quality.
I'm afraid that other than that, even for PDFs, financial outlay is required. You could certainly read through some via bookstore/Half Price Books, loaner from a friend, or even a library (some libraries have RPGs).
There is the First Steps campaign for Pathfinder Society, to be found on paizo.com under PFS Free Products.
The first part is urban, I have not played/read the other two, though they might be.
While you are there, you might also want to grab and read GM 101 and GM 201, which are two short documents on basic GMing.
You might also check out Paizo's short modules for FreeRPGDay, 4 of which (marked "PFRPG") use Pathfinder rules (the other 2 ("OGL") use D&D 3.5).