Rim brake on front and disk brake on rear Good day guys. I would like to know... I've purchased a old fixed gear bike, and i converted it to a freewheel.  I've managed to install a rim brake on front. I was going to install ine on the back but noticed theres no holes for the caliper to mount on.

Did some research, theres a way to add disk brakes on rear. But im not sure if im going to buy the disk brake adaptor... Need your opinion.. Drill hole on the frame or install disk brakes.. 

No idea on specs of the bike.. Sorry
With no disk brake mounting lugs on the frame you cannot mount disc brakes. There are bolt on adapters but I personally would not trust them. Additionally you would need a disc compatible hub which in reality means a whole new rear wheel.

You should check that that the wheel rims are compatible with rim brakes. There appear to be reflective stickers where the braking surface should be.

I always advise buying the bike you want, not a fundamentally different one hoping you can convert it. The easiest path for you might actually be to sell this bike and buy a single speed with front and rear rim brakes.