The pendlay row and bent over barbell row look similar, however there are key differences between the two exercises due to the differing starting position.
The pendlay row begins with the barbell on the floor and requires a 90-degree hip hinge so that the upper body is parallel to the floor, while the bent over row only requires a 45-degree hip hinge angle with the barbell only going down to the knees.
The greater range of motion and increased hip hinge makes the pendlay row more challenging, and most people can lift greater loads with the bent over barbell row.