I'm experienced with DnD3.0, DnD3.5, and PF1e, but I am just starting to delve into Pathfinder 2e and I have a question on Proficiency for Skills.
It says when you Level Up your character, you "Increase all of your proficiency bonuses by 1 from your new level". Does this only apply to trained (or higher) skills? Or does this apply to all Skills regardless of training? If I am untrained, why would my proficiency in that skill go up if I haven't been training in it.
If you later train in a skill at a higher level, for example my character becomes "trained" in Medicine at Level 5, would the proficiency bonus be +3 (+2 for "Trained" and +1 for the level up to 5th) or would it be +7 (+2 for "Trained" and +5 for being Level 5)? Thematically I would go with the former. If you delay training in something, you don't instantly become really good at it when you finally do start training.
Is this the same then for other things with Proficiency modifiers, such as Perception, Saving Throws, Weapons, and Armor?
Best Answer
Some of that text in leveling up seems like a holdover from the playtest when your level was always added to proficiency. Rather than using that section for explaining your proficiency bonus, lets consult the section on proficiency.
To help understand this, we can rearrange it into a table, like so:
\begin{array}{|c|c|} \hline \textbf{Proficiency} & \textbf{Bonus}\\ \hline \text{Untrained} & \text{0}\\ \hline \text{Trained} & \text{Level + 2} \\ \hline \text{Expert} & \text{Level + 4} \\ \hline \text{Master} & \text{Level + 6} \\ \hline \text{Legendary} & \text{Level + 8} \\ \hline \end{array}
So to use your example, if you go from Untrained to Trained in medicine at level 5, you would go from have a +0 bonus to a +7 bonus. This would work similarly for other proficiency modifiers as well.