Is it possible to prepare and run a Pathfinder game in the Forgotten Realms settings? Has anyone tried this?
I've found "Finding your Path in the Forgotten Realms Project" but I can't validate how useful it is.
The group I game with most of the time runs a Forgotten Realms campaign setting. We have played it in 2.0, 3.0, 3.5 and now use Pathfinder. There is very little change that we have to make. For 90-95% of it we just use the Pathfinder rules as is. We simply remade our characters for each edition as needed and custom FR specific monsters are converted to Pathfinder stats as needed. Deities and such are generally reused from the 3e/3.5e FR manuals and anything that may conflict we simply address on an as needed basis. But frankly, very little has needed to be resolved.
We are currently running the City of the Spider Queen module, which actually is a tiny bit easier in Pathfinder given the differences in rules for Haste and a couple other spells that the module relies heavily upon. Of course, our DM is making up for it in other ways.
Overall, though, it's been a fairly seamless transition for us to Pathfinder rules based in a Forgotten Realms world.
You’ll have to calculate monsters’ CMB and CMD, since 3.5 did not use those, and you’ll have to redo NPCs’ skills, since Pathfinder changed those a fair bit. You will also have to update humanoid characters’ ability scores, racial features, and class features, since Pathfinder changed a few of those, too.
This should be straightforward; just add in the things that Pathfinder added to each character’s race and class. Other than these things, you should be able to use any 3.5 content (including Forgotten Realms stuff) as-is. The conversion work is not difficult, it’s just tedious; Paizo’s claims of backwards-compatibility have... been overstated, to say the least. Adapting one thing is trivial, but when you’ve got a whole series of monsters, NPCs, and things, it becomes a lot of work for the DM, unfortunately. Easy work, just a lot of it.
The Linked Homebrew
Ultimately, that link is huge and I cannot even begin to go through it all to check it for quality. On some level, quantity may be an indicator of quality: someone who goes through the effort to write all of that out is probably also going through the effort to make it worth writing and reading – but not necessarily. I will state that Ziegander (who’s critiqued a few things later on in the thread) is a homebrewer that I have respect for, but it seems likely, given the sheer number of posts, that he has not read the entire thing either.
At any rate, it looks like the project is an attempt to create Pathfinder versions of non-Core 3.5 material as it is used in Faerûn, and possibly also to use non-Core Pathfinder material for thematically appropriate things in Faerûn. Both pretty good ideas; can’t comment on execution. The former will save you having to think too much if you come across something important that uses non-Core material that Pathfinder doesn’t have a conversion for. The latter actually introduces more work – you now have to account for more classes – but will lead to a more varied and consistent world, avoiding the usual pitfall where supplement-added classes are bizarrely absent from the gameworld.
The only thing I can say about it for certain is that you do not have to use it, and using Pathfinder for your Forgotten Realms game does not necessarily require even remotely that much work.
Pathfinder, often referred to as "D&D 3.75", is based on the D20 system and its open content, and as such is (mostly) backwards compatible with D&D 3.5, and can easily handle any D&D3.5 material you try to mix into it.
I don't see any problem with taking WotC's sourcebooks for the Forgotten Realms and either going over them to see if there aren't any irregularities, or (if you're experienced in D&D3.5 and Pathfinder) simply doing it on the fly.