I have been buying bitcoin when the price was around 400$-450$.Most of my bitcoins are bought at that price around 40 BTC and remaining at less then 600$ price.i have been holding btc in paper wallet since then and already my stash in usd is 6 times.
here is one of my tx

what i want to know is please suggest some ways to invest my bitcoin at zero risk to earn some profit.Even 0.8% to 1% profit per month is good for me but it should be risk free.i don't mind the profit percentage but risk should not be there.if you have some suggestions please post that too,if i should keep holding for more years and if yes how long should i hold?
Like everyone mentioned before me, you shouldn't think about investing them anywhere now. It is really hard to predict how everything will change through next few months, so if you would invest now you might regret doing that months later. Holding bitcoins now is not risk free of course, but i think it's still safer to keep them now instead of investing.