
Joana |

PRD>Combat>Actions in Combat>Standard Actions>Attack>Critical Hits wrote:
Increased Threat Range: Sometimes your threat range is greater than 20. That is, you can score a threat on a lower number. In such cases, a roll of lower than 20 is not an automatic hit. Any attack roll that doesn't result in a hit is not a threat.
Only a natural 20 always hits, regardless of AC.