Auto IK needs connected bones. All the bones in your rig are parented unconnected.
Your bones are set up only to deform mesh when moved but are not structured together for posing in Blender. They are just mesh deformers to be used by a different rig (in game engine) I suppose. Or you didn’t get all the rig.
Edit: All this sentence was incorrect: [ The only way to pose in Blender with this rig is to (pose mode) select all bones in chain you want to transform (ex: select all bones from finger tips to elbow to rotate arm at the elbow).] No need to select all - the bones are parented - just unconnected. What was I thinking??
Vertex weighting between bones isn’t good so if you do pose the model with these bones you’ll notice the deformation at joints is terrible.
I suppose you could build another bone structure and constrain what you’ve got to that but since these bones are just floating “mesh grabbers” you’d probably be better off starting over from scratch if you want to pose/animate this model in Blender.
Edit: See above. Btw I should’ve just answered the question. You probably already know this other info.