It depends on what grants (dis)advantage
There are many, many effects in 5th that grant (dis)advantage. (Dis)advantage is a core part of the system, and so there are tons of things that grant either of them. Whether or not adapting this to Pathfinder will break anything depends heavily on exactly what is going to grant you (dis)advantage. Here are a few examples that I think illustrate the situation.
Before I continue, I'd like to note a few numbers (thank you, AnyDice). The mean value for an advantage roll is 13.82, and there is a 51% chance of getting a number 15 or higher. The mean value for a disadvantage roll is 7.71, and there is a 49% chance of getting a number 7 or higher. The actual increase or decrease in odds between a regular roll and (dis)advantage changes depending on your target number, but if you need to roll a 10, then advantage is 25% more likely to succeed and disadvantage is 25% less likely to succeed. Because of this, I'm going to use the mathematical shorthand that (dis)advantage is a +/-5 to the roll, unless there's a specific reason to not do this.
Inspiration as a source of advantage is basically harmless. Giving players an occasional +5 to an important roll isn't going to have any long-lasting impact on the game, since it will necessarily affect a tiny number of rolls. In my experience, Inspiration only comes once every few sessions. This will have no more effect on a game than the various Action Point rules that grant small bonuses to specified rolls, like the Mythic Surge mechanic in Pathfinder.
This is where things get a bit hairy. The next logical step from granting (dis)advantage on Inspiration is to grant (dis)advantage whenever you would normally grant a +2 circumstance bonus for a beneficial circumstance. In general, this means that players will be much more likely to try and get circumstance bonuses, because they'll be worth much more. However, this generally won't have a huge effect on the game; circumstance bonuses like this aren't super common, in my experience, so adding this kind of (dis)advantage won't likely cause many problems. Watch out for players trying to game the system to get more circumstance bonuses of you do this, because if you give out these bonuses more than once a session or so, you might find that players are getting much higher checks than the system usually accounts for.
All +/-2 Bonuses/Penalties
In 5th, very few things grant a +2 bonus to a d20 roll, since that idea was phased out in favor of (dis)advantage. The logical final step for adding (dis)advantage to Pathfinder would be to replace every +2 bonus with advantage, and every -2 penalty with disadvantage. This would give you a system that looks a lot like 5th, as far as bonuses are concerned. This would have two big effects: First, there will be a much greater incentive to get those +2 bonuses, since they are almost always larger now. Flanking will be a bigger deal. Second, most effects won't stack. Since (dis)advantage doesn't stack with itself, effects that would normally stack won't under this system. That means that it's a lot harder to get the super-high bonuses that high-optimization players love. This might end up being a good thing, since stacking bonuses of various types can become a pretty big problem in some games, and this could be a good balancing factor.
There is one thing that Pathfinder has that 5th doesn't which makes adding advantage especially risky: crit-fishing builds. In 5th, it's very hard to get a large threat range. In Pathfinder, it's pretty trivial to get a 15-20 range. Normally, crit-fishing is a losing strategy, but with advantage, a 15-20 crit range means that fully half of your attacks are threats. If you only get advantage in a small number of circumstances, this isn't a big deal, but if you replace all or most +2 bonuses with advantage, this becomes a problem. This counts double if flanking gives advantage, rather than a +2 to hit. A rogue with a couple crit feats, two scimitars, and a flank buddy will be much, much more powerful with such an implementation. Basically, watch out for crit-fishing builds if you add advantage to more than a few rolls.