PAN

you need to surrender the pan card because when you deposite your old pan card then they will issue new pan card

You need not surrender the card if the PAN allotted is same but the change is in some other field like address. New PAN will be issued to you in all the cases .PAN card should be surrendered if the number itself changes

i have just changed my signature. In that case i think i'll received same PAN but my doubt is i have given just copy of my PAN not original PAN. Than i should have give original...

No need to surrender your original pan if there is only signature change

Yes...No need to surrender