My father-in-law who is handicapped moved in (from out of state) for 3-4 months and brought his sticker, can I use it in my car? Of course, we would use it only when we transport the owner of the sticker. He has 2 bad knees, recovering from a shoulder surgery, and broke his wrist, so he's just down to one hand and needs help for just about everything. Right now the plan is for him to stay long enough for him to recover, but who knows....
Those permits are valid in nearly every state, so long as they are still current and the person they are issued to is in the vehicle. I have one myself, and have used it in other states on quite a few occasions.
I don't know of any state that doesn't allow out of state permits to be used, so long as the conditions above are met. There may be a couple, never know.