It isn't going to be very easy. The difficulty that you are going to face is that WFRP doesn't align well with D&D/Pathfinder.
Some bits are going to be easier than others. Magic Items and Spells are going to be a lot easier than Races and Adversaries.
There are a few ways to consider magic items beyond the existing +1 fortune dice. These include making magic items a narrative source of advances and using magic items as free boosts.
To make items a source of advances, players buy an advance that is represented by a magic item. For instance, a piece of armor could give you the +1 Toughness advance that only worked while the armor was worn. For characteristics, this might be worth a 1xp discount. Of course, these items need would need Plot Immunity or you would have to give a refund if they were ever lost/stolen.
The other way to do it is to put advances into items and allow people to use them. Talents and action cards make sense here. This won't ramp the power level too much (lots of choice can be a negative since you have a limit of the talents and cards you can use at any time). If you were to allow these items to boost characteristic, they should add to the characteristic fortune pool instead.
Look at the Rank structure of the spells. You could possibly increase the ability of wizards and priests to buy higher ranked spells without the extra cost.
Also, if you set Equilibrium at double willpower and max at quadruple willpower, that would allow a lot more high power spells to go off. Whether you really want that to happen is up to you of course.
You are going to need to do a lot of work here. Beyond the attribute modifiers (which will be easy since they are basically the same as D&D) you've got to pick special features. Looking at what exists, most of the racial distinctions come from the allowed careers and the special mechanics of the action cards that they use.
This is going to be a lot of work for all the allowable Pathfinder races.
This is one I've not got much experience of. But you should be able to reskin most of the monsters out of the book to do similar things. Just remember to warn your players that Orcs are a bit tougher than they expect!
All that said, you should use WFRP3E to play in the Warhammer world. I do and it is a lot of fun. You should certainly play a Warhammer based game, before you start making changes, to get a better idea of how the rules as written work. They are not the easiest things to learn because they are scattered across so many books.
If you want to roleplay in a D&D style fantasy world, you would be much better off investing in Legends of Anglerre by Cubicle 7, especially if you haven't bought every last piece of WFRP. Doing this will save you weeks of work. You will also have a system that won't break when players pick two things that don't interact the way you expected them to.