if i buy bitcoin with a paypal account and then change this bitcoin wallet to another bitcoin wallet and with that wallet transfer bitcoin with somebody paypal money on another new pay^pal account, can they reach from all where it all start or every thing is lost because it is crypt ?
You need to use mixer in transfer between your first bitcoin address and second one. I will suggest you to use multiple mixing services to get enough privacy. Use one bitcoin mixing service to send from your first bitcoin address (A) to B (create new bitcoin address) and than use another mixing service to move from B to C (your second bitcoin address) in this way even if there is effort to track down the source of bitcoin, they will fail to do so.