Differences between DnD 5e and Pathfinder
5 foot step
The 5 foot step from pathfinder no longer exists. This doesn’t mean you can’t take movement that only amounts to 5 feet, it simply means that the 5 foot step you take could still provoke Attack of Opportunity.
Attacks of Opportunity.
In Pathfinder, an Attack of Opportunity could occur whenever you move around in or out of a creatures threat range. In DnD 5e, the only time an Attack of Opportunity occurs is when you leave a creatures threat range.
For instances, if you are standing right in front of an enemy, you can, on your turn, decide to move all the way around them without provoking an Attack of Opportunity, so long as you do not leave their threat range. This also means an action such as standing up from prone no longer provokes Attacks of Opportunity.
In Pathfinder, actions were broken out into Standard, Move, Full Round, Swift, and Free actions. In DnD 5e, these actions have been replaced by the following actions:
Critical Hits and Misses
In Pathfinder, the weapon you chose determined what you needed to roll to threaten a critical, and then you would re-roll to see whether the critical was successful. Likewise on a natural 1, you automatically missed, and had to roll to see if anything really bad happened.
This is not the case with DnD 5e. If you roll a natural 20, you automatically get a critical hit. The weapon you choose does not effect what die number you need to roll to get a critical. It is always only 20. On critical hit, you get to roll any of your damage dice twice before adding the relevant damage modifier.
For example, if you score a critical hit with a dagger, roll 2d4 for the damage, rather than 1d4, and then add your relevant ability modifier. If the attack involves other damage dice, such as from the rogue’s Sneak Attack feature, you roll those dice twice as well.
Critical Failures (Rolling a natural 1) still makes you automatically miss, but you do not have to roll again to see if something bad happens (unless the group decides that is a feature we want to keep in, I’m willing to house rule it :)
In Pathfinder, in order to perform a sneak attack you needed to either by flanking an appointment, or they need to be flat footed. In DnD 5e, you either need to catch them flat-footed, or another teammate needs to be threatening the same enemy, but they do not need to be directly across from you.
Think of the Proficiency Bonus as if it were your Base Attack Bonus in Pathfinder. Except instead of just applying your base attack bonus to your attacks, it applies to just about everything you do that you are “proficient in.” Proficient with a longsword that your attack with? Add your proficiency bonus. Proficient in Knowledge History? Add your proficiency bonus.