Why do you want to use the Pathfinder for this game? Doesn't fit well, maybe a variant like P6?
I could not agree more!! There are many references through out the PF materials about running low magic variants and I personally consider it an absolute SHAME that at least one solid supplement was not dedicated to to this topic.
Yes, low magic & no magic variants are 100% doable! Just get together with your party and explain this fact to them ahead of time so there are no surprises at the game table. The better you can map out what your thoughts are on how this will work ahead of time the smoother it will all work during game play and make for less ad hoc / DM Fiat at the table.
Another tip, recruit your players to help with some conversion notes for this sorta thing. DONT try to rewrite the core rule book for this, but have some working notes on what you would like to see at the game table and go from there. As an example make it a rule that only classes, races and archetypes which fit your campaign concept are allowed. I know this sounds obvious but you will be AMAZED how often I've stated similar things at my table and still had players that spent dozens of hours creating very detailed characters which DID NOT fit the (clearly stated) campaign themes.
As for the "Fan-Boy PF Club" that will very quickly tell you that PF CANT be used for this sorta thing, or that you should use a different system: Ignore them. Way back at the very beginning of time when Gygax was writing the very first versions of these rules he was very clear that if the RAW (rules as written) were not working for you, then you should wing it and go with what worked at your gaming table. This is a statement which is still echo'd in most of the rule books to this day (I think it is referred to as "Rule 0".)
I've spent literally years working on similar campaigns and I can tell you that they are very doable, however most players / GM's simply aren't willing to put in the sorta time and energy that it takes to do theses types of conversions. Frequently you have to rewrite portions of modules (I always did that anyway!) or edit monster entries, etc etc.
In the defense of the players that say "it isn't possible" I would give them some credit here and state that "it isn't possible....without a good deal for forethought and some additional leg work needed to make sure the game your about to run that week is still a balanced encounter". Also be aware that it will change your prep time before the game of only a couple of hours to anywhere between 6 - 12 hours depending on how much time you are allotting for preparation. And that is assuming that you already have a pretty solid idea of what you want your campaign's "normal" to look like.
Good luck, and feel free to hit me up via PM (or here on the forums obviously) if you wanna compare notes further.
It's actually rather easy. You just have to watch the way you build encounters, they need to realize their limits. They need to be prepared to back off from fights they can't handle, to take longer to heal than general. Focus more on physical monsters than magical threats. Demons and dragons are a lot harder to face without arcane support, but Giants and elementals are good choices. Watch out for monstrous humanoids, you really just want to be careful with special abilities all around.
And dont be afraid to simply change the creature or encounter. Dragon has SR that your party cant over come? Drop it! Change it to something else like, "dragons are magical creatures that can only be hit by XYZ materials from the age of the First Men". That material might be silver, mithril, obsidian glass, or anything else the party would be able to have reasonable access to within the confines of your campaign.
Nazgul (ref: LOTR / Tolkein) were very powerful undead, and when the party was low level they quickly had to learn how to exploit the weaknesses of such foe long before they could actually defeat them in battle. Fire and running water both served as effective weapons against them. You have to think more like an author and less like a video game player when designing these types of encounters in order to avoid a party wipe.