Hi and Welcome. My Name is ***** ***** I look forward to assisting you today with your question.
This usually happens if there is any issue with the firmware and we may need to do reinstall the firmware by factory resetting it. But we can try every possible ways to correct the issue without factory reset.
Go to Settings > Applications Manager (under More)
Swipe left or right to All tab which is next to Installed, Running etc tabs.
Find and select Android Keyboard or Samsung Keyboard or Keyboard app. Tap Clear Data. Then find Download Manager application from the list and select it. Do you see Enable button there ? If so, click Enable and restart your phone.
Please let me know if that didn't work, so we can continue troubleshooting.
Remember, this is not my final answer. If my solutions didn't work please don't rate me bad or poor. Instead please reply back to me and I will continue to help you until we fix the problem or you are satisfied.
Also go to Settings > My Device > Language and Input. Under Keyboards and Input methods, click Default button and select Samsung Keyboard.
Go back and select Samsung Keyboard, scroll down and click Reset Settings. Do the same for all keyboards there. Let me know the results please.